Abstract: Real-time Transport Protocol (RTP) and Real-time Transport Control Protocol (RTCP) of network based on real-time multimedia application were discussed at first. Then on the platform of Microsoft’s DirectShow, two sets of DirectShow filters were constructed to implement sending and receiving of audio and video data on IP network. Furthermore, a model was proposed to develop net-based real-time multimedia application, that is, COM-based programming + real-time transport protocol. Finally, the experiments showed that applications based on the model can achieve good real-time, strong error-tolerance and extensibility, high reusability and good inter-operability.