Peer to Peer(P2P) network is high dynamic, heterogeneous and low correlation degree. The cooperation of nodes is important for the P2P Network. Some researches use incentive mechanism to promote the cooperation of nodes. Different from the currently study, strong reciprocity theory was introduced to solve the non cooperation problem. Namely, there are some strong reciprocity nodes in the P2P network. Strong reciprocity nodes voluntary punished the non cooperation nodes for the fairness, even though they payed the cost themselves. The nodes’ behavior evolvement in the system was analyzed in theory. The simulation results show that the non cooperation ratio is decreased and the whole payoffs is improved in the system.