diff --git a/mybatis-flex-core/src/test/java/com/mybatisflex/core/util/StringUtilTest.java b/mybatis-flex-core/src/test/java/com/mybatisflex/core/util/StringUtilTest.java
index a133b741..a28e3992 100644
--- a/mybatis-flex-core/src/test/java/com/mybatisflex/core/util/StringUtilTest.java
+++ b/mybatis-flex-core/src/test/java/com/mybatisflex/core/util/StringUtilTest.java
@@ -1,5 +1,6 @@
 package com.mybatisflex.core.util;
 
+import com.mybatisflex.processor.util.StrUtil;
 import org.junit.Assert;
 import org.junit.Test;
 
@@ -7,27 +8,41 @@ import org.junit.Test;
 public class StringUtilTest {
 
     @Test
-    public void testCamelToUnderline(){
+    public void testCamelToUnderline() {
         String s1 = StringUtil.camelToUnderline("AAA");
-        Assert.assertEquals(s1,"aaa");
+        String s1_ = StrUtil.camelToUnderline("AAA");
+        Assert.assertEquals(s1, "aaa");
+        Assert.assertEquals(s1_, "aaa");
 
         String s2 = StringUtil.camelToUnderline("StudentIDRoom");
-        Assert.assertEquals(s2,"student_idroom");
+        String s2_ = StrUtil.camelToUnderline("StudentIDRoom");
+        Assert.assertEquals(s2, "student_idroom");
+        Assert.assertEquals(s2_, "student_idroom");
 
-        String s3 =StringUtil. camelToUnderline("StudentIdRoom");
-        Assert.assertEquals(s3,"student_id_room");
+        String s3 = StringUtil.camelToUnderline("StudentIdRoom");
+        String s3_ = StrUtil.camelToUnderline("StudentIdRoom");
+        Assert.assertEquals(s3, "student_id_room");
+        Assert.assertEquals(s3_, "student_id_room");
 
         String s4 = StringUtil.camelToUnderline("Student_ID");
-        Assert.assertEquals(s4,"student_id");
+        String s4_ = StrUtil.camelToUnderline("Student_ID");
+        Assert.assertEquals(s4, "student_id");
+        Assert.assertEquals(s4_, "student_id");
 
-        String s44 = StringUtil.camelToUnderline("StudentID");
-        Assert.assertEquals(s44,"student_id");
+        String s5 = StringUtil.camelToUnderline("StudentID");
+        String s5_ = StrUtil.camelToUnderline("StudentID");
+        Assert.assertEquals(s5, "student_id");
+        Assert.assertEquals(s5_, "student_id");
 
-        String s5 = StringUtil.camelToUnderline("Student_Id");
-        Assert.assertEquals(s5,"student_id");
+        String s6 = StringUtil.camelToUnderline("Student_Id");
+        String s6_ = StrUtil.camelToUnderline("Student_Id");
+        Assert.assertEquals(s6, "student_id");
+        Assert.assertEquals(s6_, "student_id");
 
-        String s6 = StringUtil.camelToUnderline("student_id");
-        Assert.assertEquals(s6,"student_id");
+        String s7 = StringUtil.camelToUnderline("student_id");
+        String s7_ = StrUtil.camelToUnderline("student_id");
+        Assert.assertEquals(s7, "student_id");
+        Assert.assertEquals(s7_, "student_id");
 
     }
 }
diff --git a/mybatis-flex-processor/src/main/java/com/mybatisflex/processor/util/StrUtil.java b/mybatis-flex-processor/src/main/java/com/mybatisflex/processor/util/StrUtil.java
index 34b00986..fa458f9a 100644
--- a/mybatis-flex-processor/src/main/java/com/mybatisflex/processor/util/StrUtil.java
+++ b/mybatis-flex-processor/src/main/java/com/mybatisflex/processor/util/StrUtil.java
@@ -55,7 +55,10 @@ public class StrUtil {
         for (int i = 0; i < len; i++) {
             char c = str.charAt(i);
             if (Character.isUpperCase(c) && i > 0) {
-                sb.append('_');
+                char prev = str.charAt(i - 1);
+                if (!Character.isUpperCase(prev) && prev != '_') {
+                    sb.append('_');
+                }
             }
             sb.append(Character.toLowerCase(c));
         }