diff --git a/hutool-core/src/main/java/cn/hutool/core/io/FileUtil.java b/hutool-core/src/main/java/cn/hutool/core/io/FileUtil.java
index 2eccd286e..7b06ca8be 100644
--- a/hutool-core/src/main/java/cn/hutool/core/io/FileUtil.java
+++ b/hutool-core/src/main/java/cn/hutool/core/io/FileUtil.java
@@ -3194,7 +3194,7 @@ public class FileUtil extends PathUtil {
 	public static boolean isSub(File parent, File sub) {
 		Assert.notNull(parent);
 		Assert.notNull(sub);
-		return sub.toPath().startsWith(parent.toPath());
+		return sub.toPath().toAbsolutePath().normalize().startsWith(parent.toPath().toAbsolutePath().normalize());
 	}
 
 	/**
diff --git a/hutool-core/src/test/java/cn/hutool/core/io/FileUtilTest.java b/hutool-core/src/test/java/cn/hutool/core/io/FileUtilTest.java
index 43de63973..2980d0890 100644
--- a/hutool-core/src/test/java/cn/hutool/core/io/FileUtilTest.java
+++ b/hutool-core/src/test/java/cn/hutool/core/io/FileUtilTest.java
@@ -384,4 +384,11 @@ public class FileUtilTest {
 		File file2 = new File("d:/test2/aaa");
 		Assert.assertFalse(FileUtil.isSub(file, file2));
 	}
+
+	@Test
+	public void isSubRelativeTest() {
+		File file = new File("..");
+		File file2 = new File(".");
+		Assert.assertTrue(FileUtil.isSub(file, file2));
+	}
 }