P2P systems have high scalability, robustness and fault tolerance because of its no centralized server and the network self-organized itself. As the standard protocol for VoIP and NGN, SIP is a general protocol for establishing and controlling multimedia session. In this paper, we proposed a peer to peer based realtime streaming media sharing system using SIP mechanism, which uses Chord as the underlying connection architecture. We add the media agents sever to support real time streaming media downloading. We have advanced peer and piece selection algorithm to solve the real time media stream transmission. The MPSS system architecture supports user registration, media resource location, media streaming session establishment, and realtime media streaming playback online. At last, we give a simulation and test result.