diff --git a/hutool-core/src/main/java/org/dromara/hutool/core/text/StrUtil.java b/hutool-core/src/main/java/org/dromara/hutool/core/text/StrUtil.java
index 1f6eab1fd..99f248efb 100644
--- a/hutool-core/src/main/java/org/dromara/hutool/core/text/StrUtil.java
+++ b/hutool-core/src/main/java/org/dromara/hutool/core/text/StrUtil.java
@@ -383,8 +383,14 @@ public class StrUtil extends CharSequenceUtil implements StrPool {
 	 * @return flexibleConcat
 	 */
 	public static String flexibleConcat(String str, String left, String right, String middle, int middlePos) {
+		// 预计算最终字符串的长度，避免 StringBuilder 反复扩容
+		int estimatedLength = (str != null ? str.length() : 0) +
+			(left != null ? left.length() : 0) +
+			(right != null ? right.length() : 0) +
+			(middle != null ? middle.length() : 0);
+
 		// 使用 StringBuilder 来提高拼接性能
-		StringBuilder sb = new StringBuilder();
+		StringBuilder sb = new StringBuilder(estimatedLength);
 
 		// 如果原始字符串不为 null，添加到 StringBuilder
 		if (str != null) {
@@ -394,18 +400,21 @@ public class StrUtil extends CharSequenceUtil implements StrPool {
 		// 左边拼接字符串（如果有
 		Optional.ofNullable(left)
 			.filter(s -> !s.isEmpty())
-			.ifPresent(l -> sb.insert(0, l.toCharArray()));
+			.ifPresent(l -> sb.insert(0, l));
 
 		// 右边拼接字符串（如果有）
 		Optional.ofNullable(right)
 			.filter(s -> !s.isEmpty())
 			.ifPresent(sb::append);
 
+		// 计算 middle 的插入位置
+		int adjustedMiddlePos = (left != null ? left.length() : 0) + middlePos;
+
 		// 中间拼接字符串（如果有且位置有效）
 		Optional.ofNullable(middle)
 			.filter(s -> !s.isEmpty())
-			.filter(s -> middlePos >= 0 && middlePos <= sb.length())
-			.ifPresent(m -> sb.insert(middlePos, m.toCharArray()));
+			.filter(s -> adjustedMiddlePos >= 0 && adjustedMiddlePos <= sb.length())
+			.ifPresent(m -> sb.insert(adjustedMiddlePos, m));
 
 		return sb.toString();
 	}
diff --git a/hutool-core/src/test/java/org/dromara/hutool/core/text/StrUtilTest.java b/hutool-core/src/test/java/org/dromara/hutool/core/text/StrUtilTest.java
index 3ac1499ba..2ee2ef39b 100644
--- a/hutool-core/src/test/java/org/dromara/hutool/core/text/StrUtilTest.java
+++ b/hutool-core/src/test/java/org/dromara/hutool/core/text/StrUtilTest.java
@@ -641,4 +641,20 @@ public class StrUtilTest {
 		final String s = StrUtil.indexedFormat("a{0,number,#}", 1234567);
 		Assertions.assertEquals("a1234567", s);
 	}
+
+	@Test
+	public void flexibleConcat() {
+		/**
+		 * 往左边填充
+		 */
+		System.out.println(StrUtil.flexibleConcat("hello", ">>>", null, null, -1));
+		/**
+		 * 往右边填充
+		 */
+		System.out.println(StrUtil.flexibleConcat("java", null, "!", null, -1));
+		/**
+		 * 往左右中间填充
+		 */
+		System.out.println(StrUtil.flexibleConcat("world", "abc", "xyz", "123", 3));
+	}
 }