diff --git a/sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/FileRefreshableDataSource.java b/sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/FileRefreshableDataSource.java
index 4329061144..f31177f764 100755
--- a/sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/FileRefreshableDataSource.java
+++ b/sentinel-extension/sentinel-datasource-extension/src/main/java/com/alibaba/csp/sentinel/datasource/FileRefreshableDataSource.java
@@ -118,6 +118,9 @@ public String readSource() throws Exception {
                     + ", is bigger than bufSize=" + buf.length + ". Can't read");
             }
             int len = inputStream.read(buf);
+            if (len == -1) {
+                return null;
+            }
             return new String(buf, 0, len, charset);
         } finally {
             if (inputStream != null) {