diff --git a/apps/server/src/classes/classes.service.ts b/apps/server/src/classes/classes.service.ts
index 89b3799..c69c0f1 100644
--- a/apps/server/src/classes/classes.service.ts
+++ b/apps/server/src/classes/classes.service.ts
@@ -99,6 +99,22 @@ export class ClassesService {
   async create(dto: CreateClassDto) {
     const { studentIds, teachers, dingUserIds, ...classData } = dto;
 
+    // Resolve departmentId: frontend may pass DingTalk dept ID, map to local
+    if (classData.departmentId) {
+      const localDept = await this.deptRepo.findOne({
+        where: { source: 'dingtalk', sourceId: String(classData.departmentId) },
+      });
+      if (localDept) {
+        classData.departmentId = localDept.id;
+      } else {
+        // Verify it's a valid local department ID
+        const exists = await this.deptRepo.findOne({ where: { id: classData.departmentId } });
+        if (!exists) {
+          throw new BadRequestException(`部门 ID ${classData.departmentId} 不存在`);
+        }
+      }
+    }
+
     const cls = this.classRepo.create(classData);
     const saved = await this.classRepo.save(cls);