diff --git a/Day21-30/21.文件读写和异常处理.md b/Day21-30/21.文件读写和异常处理.md
index 4d46f94..595f653 100755
--- a/Day21-30/21.文件读写和异常处理.md
+++ b/Day21-30/21.文件读写和异常处理.md
@@ -231,7 +231,7 @@ try:
         data = file1.read(512)
         while data:
             file2.write(data)
-            data = file1.read()
+            data = file1.read(512)
 except FileNotFoundError:
     print('指定的文件无法打开.')
 except IOError: