To effectively overcome the free-rider problem existing in Peer-to-Peer (P2P) network, this paper presented resource allocation scheme based on Nash bargaining which guarantees the minimum Quality of Service (QoS). Firstly, the article built the system model of the minimum QoS, analysis indicated that the cooperative peer' bargaining power is positively related to the maximum contribution ability but the non-cooperative peer' bargaining power is negative related to the maximum contribution ability, so, the cooperative peers can obtain more resources than non-cooperative peers; secondly, the article demonstrated that the cooperative peer who has larger relative bargaining power could obtain more resources than the others. Lastly, simulations show that to guarantee the peers receiving the minimum QoS, the cooperation peers resource allocation related to the initial resource allocation and the Nash bargaining power and other factors; the initial resource allocation is positively related to the maximum contribute ability of the cooperation peers, which reduces when the number of peers increases; the bargaining power decreases when the number of peers increases and resource allocation increases when the bargaining power increases. This resource allocation mechanism was compared with the classical average resource allocation mechanism which also guarantees the fairness, the cooperators can obtain more resources. The simulation results verified that the greater the bargaining power of nodes, the more resources to obtain within the minimum QoS.