In peer-to-peer video-on-demand (P2P VoD) streaming system, bandwidth is one of the most important resources. Making full use of peers' bandwidth is critical to enhance the quality of service (QoS). Thus, it is essential to design a reasonable bandwidth allocation scheme in data scheduling process. However, many data scheduling schemes do not consider bandwidth allocation in detail and have no specific bandwidth allocation schemes, which leads to the serious polarization of bandwidth allocation and unfair allocation problem. Focusing on the problem, we first present a bandwidth demand model (BDM). Based on the BDM, we apply the video dividing method to divide the video data, and according to the prefetched data and the BDM, at last we design an upload bandwidth allocation algorithm (UBAA). Simulations demonstrate that compared with LRF and RS scheme, our proposed UBAA has higher bandwidth utilization of peers, and can significantly reduce the server bandwidth costs and shorten the startup latency.