The invention relates to a system and a method for achieving quality-of-service guaranteed data distribution in a video-on-demand system based on a P2P technique, wherein by combining a P2P mode with a client-server mode, the system has better performance. In the system and the method, through the P2P mode, clients can provide services for each other so that the system has excellent expandability. When the P2P mode cannot provide satisfactory performances due to the unstability of the clients, the client-server mode is combined with the P2P mode to provide a quality-of-service guarantee for users.