Abstract: Scalability and reliability are essential to VoD. A P2P based VoD architecture (DPVoD) is proposed in this paper, which can support large-scale and reliable VoD services in the Internet. DPVoD is based on application-layer multicast, every user uses assignable-size buffer to cache the most recent video received, and provides services for later comers, and all users who share the same streaming are grouped in a multicast tree. Based on the extent of the overlap of streaming data among multicast trees, three kinds of neighbor relationships are defined. A tree may collaborately work with its neighbor trees in operations such as user joining, load balancing and fault tolerant controlling. To improve the performance of DPVoD, several mechanisms are put forward, including an efficient distributed state control protocol to exchange user state imformation efficiently, the parent selection strategy to increase the capacity of the system, and a reliable failure recovery mechanism. The problem of tail snowslide is defined for the first time. The analysis indicates that it may have a strong impact on the quality of service of VoD, and the corresponding solution is also presented. Performance analyses are carried out in theory, and the simulation results show that the proposed architecture outperforms similar systems in a number of important performance metrics such as the server stress, reliability, service ability and so on.