Abstract: The application of the anonymous communication technology is discussed. The basic concepts and terms of anonymous communication are also defined and analyzed. After discussing the classifying method of anonymous communication, according to the anonymous objects and technology adopted, a useful classification is also put forward. Then, this paper is focus on analyzing the routing-based anonymous communication system. The model of the anonymous systems and the methods used to evaluate the anonymity degree of system are studied in-depth. Finally, three practical anonymous systems, DC-NET, onion routing, and crowds, are illustrated and summarized. This results show that the anonymous communication technology is not well understood in many aspects. And its application in information security has a nice future.