diff --git a/apps/server/src/sync/sync.service.ts b/apps/server/src/sync/sync.service.ts
index 2a7469c..fdc05fe 100644
--- a/apps/server/src/sync/sync.service.ts
+++ b/apps/server/src/sync/sync.service.ts
@@ -1,7 +1,7 @@
 import { BadRequestException, Injectable, Logger } from '@nestjs/common';
 import { InjectRepository } from '@nestjs/typeorm';
 import { DataSource, Repository } from 'typeorm';
-import { SyncLog, SyncState, UserDingMapping, ClassStudent, ClassTeacher } from '../entities';
+import { SyncLog, SyncState, UserDingMapping, ClassStudent, ClassTeacher, Department } from '../entities';
 import { Class as ClassEntity } from '../entities/class.entity';
 import type { SyncPlatform, SyncType, SyncStatus } from '../entities/sync-log.entity';
 import { DingTalkService } from '../integration/dingtalk.service';
@@ -153,13 +153,32 @@ export class SyncService {
     let skipped = 0;
 
     await this.dataSource.transaction(async (manager) => {
+      // 0. 同步部门：为每个班级标记的钉钉部门创建/查找本地 Department
+      const deptLocalIdMap = new Map<number, number>(); // dingDeptId -> local deptId
+      for (const c of classItems) {
+        let dept = await manager.findOne(Department, {
+          where: { source: 'dingtalk', sourceId: String(c.deptId) },
+        });
+        if (!dept) {
+          dept = manager.create(Department, {
+            name: c.name,
+            type: 'department',
+            source: 'dingtalk',
+            sourceId: String(c.deptId),
+          });
+          dept = await manager.save(dept);
+        }
+        deptLocalIdMap.set(c.deptId, dept.id);
+      }
+
       // 1. 创建班级
       const deptClassMap = new Map<number, number>(); // deptId -> classId
       for (const c of classItems) {
-        // ponytail: Class keyword conflicts with TypeORM DeepPartial resolution
+        const deptId = deptLocalIdMap.get(c.deptId) ?? null;
         const result = await manager.save(ClassEntity, {
           name: c.name,
           code: c.code,
+          departmentId: deptId,
           classType: c.classType,
           startDate: c.startDate ?? null,
           endDate: c.endDate ?? null,
@@ -174,75 +193,119 @@ export class SyncService {
         const existingMapping = await manager.findOne(UserDingMapping, {
           where: { dingUserId: u.dingUserId },
         });
-        if (existingMapping) {
-          skipped++;
-          continue;
-        }
-
-        const username = `dd_${u.dingUserId}`;
-        const passwordHash = await bcrypt.hash('123456', 10);
-
-        const user = manager.create(User, {
-          username,
-          name: u.name,
-          passwordHash,
-          isActive: true,
-        });
-        await manager.save(user);
 
+        let userId: number | null = null;
         let isTeacher = false;
 
-        if (u.roleId != null) {
-          const role = await manager.findOne(Role, { where: { id: u.roleId } });
-          if (!role) {
-            throw new BadRequestException(`角色 id=${u.roleId} 不存在`);
-          }
-          user.roles = [role];
-          await manager.save(user);
-          isTeacher = true;
-          teacherCount++;
-        } else {
-          const student = manager.create(Student, {
-            name: u.name,
-            phone: u.mobile || undefined,
-            userId: user.id,
-            status: 'active',
+        if (existingMapping) {
+          skipped++;
+          userId = existingMapping.userId;
+          // 判断是老师还是学生：查角色
+          const existingUser = await manager.findOne(User, {
+            where: { id: userId },
+            relations: ['roles'],
           });
-          await manager.save(student);
-          studentCount++;
+          isTeacher = (existingUser?.roles?.length ?? 0) > 0;
+        } else {
+          // 检查是否已存在（syncAll 或历史导入），避免撞 username 唯一约束
+          const username = `dd_${u.dingUserId}`;
+          const whereConditions: Record<string, unknown>[] = [{ username }];
+          if (u.mobile) whereConditions.push({ username: u.mobile });
+          let user = await manager.findOne(User, { where: whereConditions });
+
+          if (!user) {
+            const passwordHash = await bcrypt.hash('123456', 10);
+            user = manager.create(User, {
+              username,
+              name: u.name,
+              passwordHash,
+              isActive: true,
+            });
+            await manager.save(user);
+          } else {
+            // 已存在：更新姓名
+            user.name = u.name;
+            await manager.save(user);
+          }
+          userId = user.id;
+
+          // 解析学生所属部门
+          const studentDeptId = u.roleId == null && classItems.length > 0 && u.dingDeptIds?.length > 0
+            ? deptLocalIdMap.get(u.dingDeptIds.find((d) => deptLocalIdMap.has(d)) ?? -1) ?? undefined
+            : undefined;
+
+          if (u.roleId != null) {
+            const role = await manager.findOne(Role, { where: { id: u.roleId } });
+            if (!role) throw new BadRequestException(`角色 id=${u.roleId} 不存在`);
+            user.roles = [role];
+            await manager.save(user);
+            isTeacher = true;
+            teacherCount++;
+          } else {
+            // 学生：检查 Student 是否已存在，不存在则创建
+            let student = await manager.findOne(Student, { where: { userId: user.id } });
+            if (!student) {
+              student = manager.create(Student, {
+                name: u.name,
+                phone: u.mobile || undefined,
+                userId: user.id,
+                departmentId: studentDeptId,
+                status: 'active',
+              });
+              await manager.save(student);
+            }
+            studentCount++;
+          }
+
+          // 钉钉映射（幂等：可能已被 syncAll 创建）
+          const existingMappingForUser = await manager.findOne(UserDingMapping, {
+            where: { dingUserId: u.dingUserId },
+          });
+          if (!existingMappingForUser) {
+            const mapping = manager.create(UserDingMapping, {
+              dingUserId: u.dingUserId,
+              userId: user.id,
+              dingName: u.name,
+              dingMobile: u.mobile,
+            });
+            await manager.save(mapping);
+          }
         }
 
-        // 钉钉映射
-        const mapping = manager.create(UserDingMapping, {
-          dingUserId: u.dingUserId,
-          userId: user.id,
-          dingName: u.name,
-          dingMobile: u.mobile,
-        });
-        await manager.save(mapping);
-
-        // 3. 建立班级关联
+        // 3. 建立班级关联（新建/已存在用户都处理）
         if (classItems.length > 0 && u.dingDeptIds?.length > 0) {
           for (const deptId of u.dingDeptIds) {
             const classId = deptClassMap.get(deptId);
-            if (!classId) continue; // 该部门未标为班级
+            if (!classId) continue;
 
             if (isTeacher) {
-              const ct = manager.create(ClassTeacher, {
-                classId,
-                userId: user.id,
-                roleType: 'teacher',
+              const existingCT = await manager.findOne(ClassTeacher, {
+                where: { classId, userId },
               });
-              await manager.save(ct);
+              if (!existingCT) {
+                const ct = manager.create(ClassTeacher, {
+                  classId,
+                  userId,
+                  roleType: 'teacher',
+                });
+                await manager.save(ct);
+              }
             } else {
-              const studentRecord = await manager.findOne(Student, { where: { userId: user.id } });
-              if (!studentRecord) continue;
-              const cs = manager.create(ClassStudent, {
-                classId,
-                studentId: studentRecord.id,
-                status: 'active',
+              const studentRecord = await manager.findOne(Student, {
+                where: { userId },
               });
-              await manager.save(cs);
+              if (!studentRecord) continue;
+              const existingCS = await manager.findOne(ClassStudent, {
+                where: { classId, studentId: studentRecord.id },
+              });
+              if (!existingCS) {
+                const cs = manager.create(ClassStudent, {
+                  classId,
+                  studentId: studentRecord.id,
+                  status: 'active',
+                });
+                await manager.save(cs);
+              }
             }
           }
         }