diff --git a/logs/file.go b/logs/file.go
index 6fa2935b..4f228267 100644
--- a/logs/file.go
+++ b/logs/file.go
@@ -195,7 +195,7 @@ func (w *fileLogWriter) lines() (int, error) {
 }
 
 // DoRotate means it need to write file in new file.
-// new file name like xx.2013-01-01.2.log
+// new file name like xx.2013-01-01.log (daily) or xx.001.log (by line or size)
 func (w *fileLogWriter) doRotate(logTime time.Time) error {
 	_, err := os.Lstat(w.Filename)
 	if err != nil {