diff --git a/global/net.go b/global/net.go
index c72000a..6011232 100644
--- a/global/net.go
+++ b/global/net.go
@@ -184,7 +184,7 @@ func DownloadFileMultiThreading(url, path string, limit int64, threadCount int,
 			req.Header.Set(k, v)
 		}
 
-		if _, ok := headers["User-Agent"]; ok {
+		if _, ok := headers["User-Agent"]; !ok {
 			req.Header["User-Agent"] = []string{UserAgent}
 		}
 		req.Header.Set("range", "bytes="+strconv.FormatInt(block.BeginOffset, 10)+"-"+strconv.FormatInt(block.EndOffset, 10))