As demands for streaming video and audio over the Internet gains more and more popularity, proper caching of multimedia streams has become increasingly important. Previous researches on caching proxy have not addressed the problem of single stream image and stream network prefetch. In this paper, we discuss principles and mechanism of SSI in detail. Specifically, we give corresponding modification algorithms for receiving and sending streaming data in the caching proxy. After analyzing of different scenarios of stream network prefetch, we present a theoretical model of stream network prefetch. According to this model, we propose an effective stream network prefetch policy based on RTCP packets feedback and RTP packets network delay. Testing results show that our proposed mechanisms are valid and effective.