diff --git a/backend/src/main/java/com/designhub/service/UserService.java b/backend/src/main/java/com/designhub/service/UserService.java
index 2d79335..459fe24 100644
--- a/backend/src/main/java/com/designhub/service/UserService.java
+++ b/backend/src/main/java/com/designhub/service/UserService.java
@@ -678,12 +678,29 @@ public class UserService {
                 }
             }
             
-            // 3. 查找或创建用户（使用unionId作为唯一标识）
+            // 3. 查找或创建用户
+            // 🔥 优先通过ding_user_id查找（处理旧用户数据），其次通过unionId生成的email查找
             String email = "dingtalk_" + unionId + "@dingtalk.local";
-            User user = userMapper.selectOne(
-                new LambdaQueryWrapper<User>()
-                    .eq(User::getEmail, email)
-            );
+            User user = null;
+            
+            // 优先通过钉钉用户ID查找
+            if (dingtalkUserId != null) {
+                user = userMapper.selectOne(
+                    new LambdaQueryWrapper<User>()
+                        .eq(User::getDingUserId, dingtalkUserId)
+                );
+                if (user != null) {
+                    log.info("通过ding_user_id找到已有用户（免登）: userId={}, realName={}", user.getId(), user.getRealName());
+                }
+            }
+            
+            // 如果通过ding_user_id找不到，再通过email查找
+            if (user == null) {
+                user = userMapper.selectOne(
+                    new LambdaQueryWrapper<User>()
+                        .eq(User::getEmail, email)
+                );
+            }
             
             if (user == null) {
                 // 首次登录：创建用户
@@ -809,12 +826,28 @@ public class UserService {
             }
             
             // 4. 查找或创建用户
-            // 使用unionId作为唯一标识
+            // 优先通过ding_user_id查找（更可靠），其次通过unionId生成的email查找
             String email = "dingtalk_" + unionId + "@dingtalk.local";
-            User user = userMapper.selectOne(
-                new LambdaQueryWrapper<User>()
-                    .eq(User::getEmail, email)
-            );
+            User user = null;
+            
+            // 🔥 优先通过钉钉用户ID查找（处理旧用户数据）
+            if (dingtalkUserId != null) {
+                user = userMapper.selectOne(
+                    new LambdaQueryWrapper<User>()
+                        .eq(User::getDingUserId, dingtalkUserId)
+                );
+                if (user != null) {
+                    log.info("通过ding_user_id找到已有用户: userId={}, realName={}", user.getId(), user.getRealName());
+                }
+            }
+            
+            // 如果通过ding_user_id找不到，再通过email查找
+            if (user == null) {
+                user = userMapper.selectOne(
+                    new LambdaQueryWrapper<User>()
+                        .eq(User::getEmail, email)
+                );
+            }
             
             if (user == null) {
                 // 首次登录：创建用户但不分配部门