diff --git a/README.md b/README.md
index c02f7f9..bd699e6 100644
--- a/README.md
+++ b/README.md
@@ -49,4 +49,5 @@ EQUAL,somedomain
 ## Debug info
 
 * the `ja-netfilter` will **NOT** output debugging information by default
-* add environment variable `JANF_DEBUG=1` and start to enable it
\ No newline at end of file
+* add environment variable `JANF_DEBUG=1` and start to enable it
+* or add system property `-Djanf.debug=1` to enable it
\ No newline at end of file
diff --git a/src/main/java/io/zhile/research/ja/netfilter/commons/DebugInfo.java b/src/main/java/io/zhile/research/ja/netfilter/commons/DebugInfo.java
index 027c99b..803a89c 100644
--- a/src/main/java/io/zhile/research/ja/netfilter/commons/DebugInfo.java
+++ b/src/main/java/io/zhile/research/ja/netfilter/commons/DebugInfo.java
@@ -3,7 +3,7 @@ package io.zhile.research.ja.netfilter.commons;
 import io.zhile.research.ja.netfilter.utils.DateUtils;
 
 public class DebugInfo {
-    private static final boolean DEBUG = "1".equals(System.getenv("JANF_DEBUG"));
+    private static final boolean DEBUG = "1".equals(System.getenv("JANF_DEBUG")) || "1".equals(System.getProperty("janf.debug"));
 
     public static void output(String content) { // No logger lib required
         if (!DEBUG) {