P2P Streaming has a Real-time requirement. In the Mesh-based network, the bandwidth of fresh peers who join the network is insufficient because of lacking of data copy, and the Real-time requirement couldn't be satisfied. Therefore, the peers have to request media data from media server to satisfy the Real-time requirement which will consume a large amount of media server's bandwidth. In this paper, we firstly model the network scale of P2P streaming both in live and VoD scenarios, based on which we propose the factors that affect the network scale and analyze the different effects of these factors in live and VoD scenarios.