diff --git a/backend/src/main/java/com/xly/test4/module/usr/service/impl/UserServiceImpl.java b/backend/src/main/java/com/xly/test4/module/usr/service/impl/UserServiceImpl.java
index f0d5e93..bfb4de3 100644
--- a/backend/src/main/java/com/xly/test4/module/usr/service/impl/UserServiceImpl.java
+++ b/backend/src/main/java/com/xly/test4/module/usr/service/impl/UserServiceImpl.java
@@ -1,5 +1,8 @@
 package com.xly.test4.module.usr.service.impl;
 
+import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
+import com.xly.test4.common.exception.BusinessException;
+import com.xly.test4.common.response.ResultCode;
 import com.xly.test4.common.security.CurrentUser;
 import com.xly.test4.common.security.CurrentUserContext;
 import com.xly.test4.module.usr.converter.UserConverter;
@@ -36,6 +39,15 @@ public class UserServiceImpl implements UserService {
     public UserCreateVO createUser(UserCreateDTO dto) {
         CurrentUser current = CurrentUserContext.current();
 
+        if (userMapper.selectCount(new LambdaQueryWrapper<User>()
+                .eq(User::getSUserName, dto.getUserName())) > 0) {
+            throw new BusinessException(ResultCode.USER_NAME_DUPLICATE, "用户名已存在");
+        }
+        if (userMapper.selectCount(new LambdaQueryWrapper<User>()
+                .eq(User::getSUserCode, dto.getUserCode())) > 0) {
+            throw new BusinessException(ResultCode.USER_CODE_DUPLICATE, "用户号已存在");
+        }
+
         User user = userConverter.toEntity(dto);
         user.setSBrandsId(current.getBrandsId());
         user.setSSubsidiaryId(current.getSubsidiaryId());
diff --git a/backend/src/test/java/com/xly/test4/module/usr/service/impl/UserServiceImplTest.java b/backend/src/test/java/com/xly/test4/module/usr/service/impl/UserServiceImplTest.java
index b8ff942..f3727cf 100644
--- a/backend/src/test/java/com/xly/test4/module/usr/service/impl/UserServiceImplTest.java
+++ b/backend/src/test/java/com/xly/test4/module/usr/service/impl/UserServiceImplTest.java
@@ -1,5 +1,7 @@
 package com.xly.test4.module.usr.service.impl;
 
+import com.baomidou.mybatisplus.core.conditions.Wrapper;
+import com.xly.test4.common.exception.BusinessException;
 import com.xly.test4.common.security.CurrentUser;
 import com.xly.test4.common.security.CurrentUserContext;
 import com.xly.test4.module.usr.converter.UserConverter;
@@ -18,9 +20,12 @@ import org.springframework.security.crypto.password.PasswordEncoder;
 import java.util.List;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.mockStatic;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 class UserServiceImplTest {
@@ -64,6 +69,7 @@ class UserServiceImplTest {
         return dto;
     }
 
+    @SuppressWarnings("unchecked")
     private void stubConverterReturnsEmptyUser() {
         when(userConverter.toEntity(any(UserCreateDTO.class))).thenAnswer(inv -> new User());
         when(userConverter.toVO(any(User.class))).thenAnswer(inv -> {
@@ -75,6 +81,7 @@ class UserServiceImplTest {
             u.setIIncrement(42);
             return 1;
         });
+        when(userMapper.selectCount(any(Wrapper.class))).thenReturn(0L);
     }
 
     @Test
@@ -110,7 +117,37 @@ class UserServiceImplTest {
         service.createUser(dto);
 
         ArgumentCaptor<User> captor = ArgumentCaptor.forClass(User.class);
-        org.mockito.Mockito.verify(userMapper).insert(captor.capture());
+        verify(userMapper).insert(captor.capture());
         assertThat(passwordEncoder.matches("666666", captor.getValue().getSPasswordHash())).isTrue();
     }
+
+    @Test
+    @SuppressWarnings("unchecked")
+    void createUser_duplicateUserName_throws40002() {
+        stubConverterReturnsEmptyUser();
+        // 第一次 selectCount(对 sUserName) 返回 > 0 → 触发 40002
+        when(userMapper.selectCount(any(Wrapper.class))).thenReturn(1L);
+
+        assertThatThrownBy(() -> service.createUser(baseDTO()))
+                .isInstanceOf(BusinessException.class)
+                .matches(e -> ((BusinessException) e).getCode() == 40002);
+
+        verify(userMapper, never()).insert(any(User.class));
+    }
+
+    @Test
+    @SuppressWarnings("unchecked")
+    void createUser_duplicateUserCode_throws40003() {
+        stubConverterReturnsEmptyUser();
+        // 第一次 selectCount(userName)=0,第二次(userCode)=1
+        when(userMapper.selectCount(any(Wrapper.class)))
+                .thenReturn(0L)
+                .thenReturn(1L);
+
+        assertThatThrownBy(() -> service.createUser(baseDTO()))
+                .isInstanceOf(BusinessException.class)
+                .matches(e -> ((BusinessException) e).getCode() == 40003);
+
+        verify(userMapper, never()).insert(any(User.class));
+    }
 }