diff --git a/What-is-rule-file-and-how-to-write-one.md b/What-is-rule-file-and-how-to-write-one.md
index 5f3ce2f..cbfe660 100644
--- a/What-is-rule-file-and-how-to-write-one.md
+++ b/What-is-rule-file-and-how-to-write-one.md
@@ -104,6 +104,17 @@ To invoke a rule file
 * in shell ``anyproxy --rule /path/to/ruleFile.js``
 
 
+To invoke a third-party node module in rule file
+-------------------------
+* ``` anyproxy install ``` is designed for quickly invoking third-party modules in rule file
+* for example, if you want to use *underscore* for supporting rules development, just use ``` anyproxy install underscore ```...
+* ... and require it in rule file
+
+```
+var base = require("path").join(process.env.NODE_PATH,'anyproxy','node_modules');
+var underscore = require(path.join(base,'underscore'));
+```
+
 Samples
 -------------------------
 * Samples could be found at [https://github.com/alibaba/anyproxy/tree/master/rule_sample](https://github.com/alibaba/anyproxy/tree/master/rule_sample).
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