diff --git a/apps/api/src/app.module.ts b/apps/api/src/app.module.ts
index 4f6ee3f..8c2a78f 100644
--- a/apps/api/src/app.module.ts
+++ b/apps/api/src/app.module.ts
@@ -3,6 +3,7 @@ import { ConfigModule } from "@nestjs/config";
 import { AttachmentModule } from "./attachment/attachment.module";
 import { AuthModule } from "./auth/auth.module";
 import { PrismaModule } from "./prisma/prisma.module";
+import { SyncModule } from "./sync/sync.module";
 import { TaskModule } from "./task/task.module";
 
 @Module({
@@ -14,7 +15,8 @@ import { TaskModule } from "./task/task.module";
     PrismaModule,
     AuthModule,
     TaskModule,
-    AttachmentModule
+    AttachmentModule,
+    SyncModule
   ]
 })
 export class AppModule {}
diff --git a/apps/api/src/sync/dto/sync-push.dto.ts b/apps/api/src/sync/dto/sync-push.dto.ts
new file mode 100644
index 0000000..91b3a06
--- /dev/null
+++ b/apps/api/src/sync/dto/sync-push.dto.ts
@@ -0,0 +1,62 @@
+import { Type } from "class-transformer";
+import {
+  ArrayMaxSize,
+  ArrayMinSize,
+  IsArray,
+  IsEnum,
+  IsInt,
+  IsOptional,
+  IsString,
+  MaxLength,
+  Min,
+  ValidateNested
+} from "class-validator";
+
+export enum SyncEntityTypeDto {
+  TASK = "TASK"
+}
+
+export enum SyncActionTypeDto {
+  CREATE = "CREATE",
+  UPDATE = "UPDATE",
+  DELETE = "DELETE"
+}
+
+export class SyncPushOperationDto {
+  @IsString()
+  @MaxLength(64)
+  opId!: string;
+
+  @IsString()
+  @MaxLength(64)
+  entityId!: string;
+
+  @IsEnum(SyncEntityTypeDto)
+  entityType!: SyncEntityTypeDto;
+
+  @IsEnum(SyncActionTypeDto)
+  action!: SyncActionTypeDto;
+
+  @IsOptional()
+  @IsString()
+  @MaxLength(50000)
+  payload?: string;
+
+  @Type(() => Number)
+  @IsInt()
+  @Min(0)
+  clientTs!: number;
+
+  @IsString()
+  @MaxLength(128)
+  deviceId!: string;
+}
+
+export class SyncPushDto {
+  @IsArray()
+  @ArrayMinSize(1)
+  @ArrayMaxSize(200)
+  @ValidateNested({ each: true })
+  @Type(() => SyncPushOperationDto)
+  operations!: SyncPushOperationDto[];
+}
diff --git a/apps/api/src/sync/sync.controller.ts b/apps/api/src/sync/sync.controller.ts
new file mode 100644
index 0000000..58ec30c
--- /dev/null
+++ b/apps/api/src/sync/sync.controller.ts
@@ -0,0 +1,25 @@
+import { Body, Controller, Headers, Post, UnauthorizedException } from "@nestjs/common";
+import { SyncPushDto } from "./dto/sync-push.dto";
+import { SyncPushResponse, SyncService } from "./sync.service";
+
+@Controller("sync")
+export class SyncController {
+  constructor(private readonly syncService: SyncService) {}
+
+  @Post("push")
+  async pushOperations(
+    @Headers("x-user-id") userIdHeader: string | string[] | undefined,
+    @Body() body: SyncPushDto
+  ): Promise<SyncPushResponse> {
+    return this.syncService.pushOperations(this.resolveUserId(userIdHeader), body);
+  }
+
+  private resolveUserId(userIdHeader: string | string[] | undefined): string {
+    const userId = Array.isArray(userIdHeader) ? userIdHeader[0] : userIdHeader;
+    if (!userId) {
+      throw new UnauthorizedException("缺少用户上下文");
+    }
+
+    return userId;
+  }
+}
diff --git a/apps/api/src/sync/sync.module.ts b/apps/api/src/sync/sync.module.ts
new file mode 100644
index 0000000..65f1492
--- /dev/null
+++ b/apps/api/src/sync/sync.module.ts
@@ -0,0 +1,11 @@
+import { Module } from "@nestjs/common";
+import { PrismaModule } from "../prisma/prisma.module";
+import { SyncController } from "./sync.controller";
+import { SyncService } from "./sync.service";
+
+@Module({
+  imports: [PrismaModule],
+  controllers: [SyncController],
+  providers: [SyncService]
+})
+export class SyncModule {}
diff --git a/apps/api/src/sync/sync.service.ts b/apps/api/src/sync/sync.service.ts
new file mode 100644
index 0000000..1dac744
--- /dev/null
+++ b/apps/api/src/sync/sync.service.ts
@@ -0,0 +1,149 @@
+import { Injectable } from "@nestjs/common";
+import { Prisma } from "../../generated/prisma/client";
+import { PrismaService } from "../prisma/prisma.service";
+import { SyncPushDto, SyncPushOperationDto } from "./dto/sync-push.dto";
+
+export type SyncPushItemStatus = "accepted" | "duplicate" | "failed";
+
+export type SyncPushItemResult = {
+  opId: string;
+  status: SyncPushItemStatus;
+  serverTs: string | null;
+  reason: string | null;
+};
+
+export type SyncPushResponse = {
+  acceptedCount: number;
+  duplicateCount: number;
+  failedCount: number;
+  results: SyncPushItemResult[];
+};
+
+type ExistingOperationRecord = {
+  opId: string;
+  serverTs: Date;
+};
+
+@Injectable()
+export class SyncService {
+  constructor(private readonly prismaService: PrismaService) {}
+
+  async pushOperations(userId: string, body: SyncPushDto): Promise<SyncPushResponse> {
+    const existingOperations = await this.loadExistingOperations(userId, body.operations);
+    const results: SyncPushItemResult[] = [];
+    const seenOperationIds = new Set<string>();
+    const acceptedOperationServerTs = new Map<string, string>();
+
+    for (const operation of body.operations) {
+      if (seenOperationIds.has(operation.opId)) {
+        results.push({
+          opId: operation.opId,
+          status: "duplicate",
+          serverTs: acceptedOperationServerTs.get(operation.opId) ?? null,
+          reason: "same_batch_duplicate"
+        });
+        continue;
+      }
+
+      seenOperationIds.add(operation.opId);
+
+      const existingOperation = existingOperations.get(operation.opId);
+      if (existingOperation) {
+        results.push({
+          opId: operation.opId,
+          status: "duplicate",
+          serverTs: existingOperation.serverTs.toISOString(),
+          reason: "already_synced"
+        });
+        continue;
+      }
+
+      try {
+        const createdOperation = await this.prismaService.syncOperation.create({
+          data: {
+            opId: operation.opId,
+            userId,
+            deviceId: operation.deviceId,
+            entityType: operation.entityType,
+            entityId: operation.entityId,
+            action: operation.action,
+            payload: operation.payload,
+            clientTs: new Date(operation.clientTs)
+          },
+          select: {
+            opId: true,
+            serverTs: true
+          }
+        });
+
+        const serverTs = createdOperation.serverTs.toISOString();
+        acceptedOperationServerTs.set(createdOperation.opId, serverTs);
+        results.push({
+          opId: createdOperation.opId,
+          status: "accepted",
+          serverTs,
+          reason: null
+        });
+      } catch (error) {
+        if (this.isDuplicateOpIdError(error)) {
+          results.push({
+            opId: operation.opId,
+            status: "duplicate",
+            serverTs: null,
+            reason: "already_synced"
+          });
+          continue;
+        }
+
+        results.push({
+          opId: operation.opId,
+          status: "failed",
+          serverTs: null,
+          reason: "persist_failed"
+        });
+      }
+    }
+
+    return {
+      acceptedCount: results.filter((item) => item.status === "accepted").length,
+      duplicateCount: results.filter((item) => item.status === "duplicate").length,
+      failedCount: results.filter((item) => item.status === "failed").length,
+      results
+    };
+  }
+
+  private async loadExistingOperations(
+    userId: string,
+    operations: SyncPushOperationDto[]
+  ): Promise<Map<string, ExistingOperationRecord>> {
+    const opIds = Array.from(new Set(operations.map((operation) => operation.opId)));
+
+    const existingOperations = (await this.prismaService.syncOperation.findMany({
+      where: {
+        userId,
+        opId: {
+          in: opIds
+        }
+      },
+      select: {
+        opId: true,
+        serverTs: true
+      }
+    })) as ExistingOperationRecord[];
+
+    return new Map(
+      existingOperations.map((operation): [string, ExistingOperationRecord] => [
+        operation.opId,
+        operation
+      ])
+    );
+  }
+
+  private isDuplicateOpIdError(error: unknown): boolean {
+    if (!(error instanceof Prisma.PrismaClientKnownRequestError)) {
+      return false;
+    }
+
+    return error.code === "P2002";
+  }
+}
diff --git a/apps/api/test/sync-push.spec.ts b/apps/api/test/sync-push.spec.ts
new file mode 100644
index 0000000..c14976b
--- /dev/null
+++ b/apps/api/test/sync-push.spec.ts
@@ -0,0 +1,233 @@
+import request from "supertest";
+import { INestApplication, ValidationPipe } from "@nestjs/common";
+import { Test, TestingModule } from "@nestjs/testing";
+import { PrismaService } from "../src/prisma/prisma.service";
+import { SyncController } from "../src/sync/sync.controller";
+import { SyncService } from "../src/sync/sync.service";
+
+type SyncOperationRecord = {
+  id: string;
+  opId: string;
+  userId: string;
+  deviceId: string;
+  entityType: string;
+  entityId: string;
+  action: string;
+  payload?: string;
+  clientTs: Date;
+  serverTs: Date;
+};
+
+class InMemoryPrismaService {
+  private syncOperationIdSequence = 1;
+  private syncOperations: SyncOperationRecord[] = [];
+
+  readonly syncOperation = {
+    findMany: async (args: {
+      where: {
+        userId: string;
+        opId: {
+          in: string[];
+        };
+      };
+      select: {
+        opId: true;
+        serverTs: true;
+      };
+    }) => {
+      return this.syncOperations
+        .filter(
+          (item) => item.userId === args.where.userId && args.where.opId.in.includes(item.opId)
+        )
+        .map((item) => ({
+          opId: item.opId,
+          serverTs: item.serverTs
+        }));
+    },
+
+    create: async (args: {
+      data: {
+        opId: string;
+        userId: string;
+        deviceId: string;
+        entityType: string;
+        entityId: string;
+        action: string;
+        payload?: string;
+        clientTs: Date;
+      };
+      select: {
+        opId: true;
+        serverTs: true;
+      };
+    }) => {
+      const createdOperation: SyncOperationRecord = {
+        id: `sync_${this.syncOperationIdSequence++}`,
+        opId: args.data.opId,
+        userId: args.data.userId,
+        deviceId: args.data.deviceId,
+        entityType: args.data.entityType,
+        entityId: args.data.entityId,
+        action: args.data.action,
+        payload: args.data.payload,
+        clientTs: args.data.clientTs,
+        serverTs: new Date()
+      };
+
+      this.syncOperations.push(createdOperation);
+
+      return {
+        opId: createdOperation.opId,
+        serverTs: createdOperation.serverTs
+      };
+    }
+  };
+
+  getOperationCount(): number {
+    return this.syncOperations.length;
+  }
+}
+
+describe("SyncController (integration)", () => {
+  let app: INestApplication;
+  let prismaService: InMemoryPrismaService;
+
+  beforeAll(async () => {
+    prismaService = new InMemoryPrismaService();
+
+    const moduleRef: TestingModule = await Test.createTestingModule({
+      controllers: [SyncController],
+      providers: [SyncService, { provide: PrismaService, useValue: prismaService }]
+    }).compile();
+
+    app = moduleRef.createNestApplication();
+    app.useGlobalPipes(
+      new ValidationPipe({
+        transform: true,
+        whitelist: true,
+        forbidNonWhitelisted: true
+      })
+    );
+    await app.init();
+  });
+
+  afterAll(async () => {
+    await app.close();
+  });
+
+  it("should accept operations once and mark repeated push as duplicate", async () => {
+    const payload = {
+      operations: [
+        {
+          opId: "op-create-1",
+          entityType: "TASK",
+          entityId: "task-1",
+          action: "CREATE",
+          payload: '{"title":"任务一"}',
+          clientTs: 1712419200000,
+          deviceId: "device-a"
+        },
+        {
+          opId: "op-update-1",
+          entityType: "TASK",
+          entityId: "task-1",
+          action: "UPDATE",
+          payload: '{"title":"任务一-更新"}',
+          clientTs: 1712419201000,
+          deviceId: "device-a"
+        }
+      ]
+    };
+
+    const firstResponse = await request(app.getHttpServer())
+      .post("/sync/push")
+      .set("x-user-id", "user-1")
+      .send(payload)
+      .expect(201);
+
+    expect(firstResponse.body.acceptedCount).toBe(2);
+    expect(firstResponse.body.duplicateCount).toBe(0);
+    expect(firstResponse.body.failedCount).toBe(0);
+    expect(firstResponse.body.results).toEqual([
+      expect.objectContaining({
+        opId: "op-create-1",
+        status: "accepted"
+      }),
+      expect.objectContaining({
+        opId: "op-update-1",
+        status: "accepted"
+      })
+    ]);
+    expect(prismaService.getOperationCount()).toBe(2);
+
+    const secondResponse = await request(app.getHttpServer())
+      .post("/sync/push")
+      .set("x-user-id", "user-1")
+      .send(payload)
+      .expect(201);
+
+    expect(secondResponse.body.acceptedCount).toBe(0);
+    expect(secondResponse.body.duplicateCount).toBe(2);
+    expect(secondResponse.body.failedCount).toBe(0);
+    expect(secondResponse.body.results).toEqual([
+      expect.objectContaining({
+        opId: "op-create-1",
+        status: "duplicate",
+        reason: "already_synced"
+      }),
+      expect.objectContaining({
+        opId: "op-update-1",
+        status: "duplicate",
+        reason: "already_synced"
+      })
+    ]);
+    expect(prismaService.getOperationCount()).toBe(2);
+  });
+
+  it("should mark duplicated op ids in the same batch as duplicate", async () => {
+    const response = await request(app.getHttpServer())
+      .post("/sync/push")
+      .set("x-user-id", "user-2")
+      .send({
+        operations: [
+          {
+            opId: "op-dup-1",
+            entityType: "TASK",
+            entityId: "task-2",
+            action: "CREATE",
+            payload: '{"title":"任务二"}',
+            clientTs: 1712419300000,
+            deviceId: "device-b"
+          },
+          {
+            opId: "op-dup-1",
+            entityType: "TASK",
+            entityId: "task-2",
+            action: "UPDATE",
+            payload: '{"title":"任务二-重复"}',
+            clientTs: 1712419301000,
+            deviceId: "device-b"
+          }
+        ]
+      })
+      .expect(201);
+
+    expect(response.body.acceptedCount).toBe(1);
+    expect(response.body.duplicateCount).toBe(1);
+    expect(response.body.failedCount).toBe(0);
+    expect(response.body.results[0]).toEqual(
+      expect.objectContaining({
+        opId: "op-dup-1",
+        status: "accepted"
+      })
+    );
+    expect(response.body.results[1]).toEqual(
+      expect.objectContaining({
+        opId: "op-dup-1",
+        status: "duplicate",
+        reason: "same_batch_duplicate"
+      })
+    );
+    expect(prismaService.getOperationCount()).toBe(3);
+  });
+});