In the system of 3G IMS, SIP application server is the main provider for enriching the content of service. JCP(Java Community Process)defines SIP Servlet Standard to simplify the process and improve the efficiency, which also offers Java application programming interface(API)for SIP application server. The mechanism of application router for SIP Servlet is an important module for rapidly customizing 3G services and it is a hotspot of studying nowadays. In order to implement complex services by composing applications flexibly, this article based on analyzing the application router for SIP Servlet puts forward and realizes a method, which makes use of SailfinV2 standard container to design the custom defined application router, and also expounds how to employ the method according to an instance. Finally, the experiment result reflects the high efficiency and flexibility of newly increased mechanism of application router.