diff --git a/demo/up.php b/demo/up.php
index 22d12fae..3f52e257 100644
--- a/demo/up.php
+++ b/demo/up.php
@@ -5,7 +5,7 @@
 
 $bucket = 'rwxf';
 $key = 'up.php';
-$file = __FILE__;
+$file = __FILE__;  //path to local file
 
 
 $client = new Qiniu_MacHttpClient(null);