Abstract: This article describes the design and realization process about a simple instant messaging system based on the P2P. This system implementes the functions of realtime information transmission as well as the file transferring for the online users on the network. The system uses the mixed P2P pattern, in which the server program adopts the multithread technology used in the identification authentication and the inquiry about condition information when registering clients. The information communication on the P2P network is carried on directly among the clients. The instant messaging system based on the P2P has many advantages. It is convenient, effective, inexpensive, instant and so on. Therefore it is rapidly becoming an important tool for the application during the individuals and enterprises.

Key words: P2P, instant message, communication protocol, model