At present, it is lack effective mechanism to impro ve the security of the system in the P2P network. T here is a lot of malicious behaviors. Network security model has bec ome an important subject of P2P application researc h. This paper will study P2P network based on group trust r elationship. Set up different groups according to t he node interests. The overall trust is compounded by direc t trust between nodes, trust between groups and nod es, trust between groups and multiple parameters. Through the simulation experiment, this model is verified to h ave high ratio of successful download, and the peer load can be controlled in a admissible range. The performan ce of this model is studied through simulation experiment. The results show that the model can identify malicious nodes effectively. According to the trust value of the re sponder select the download source. In the P2P netw ork, cooperative nodes have the high request rate of suc cess and node degree of satisfaction in different m alicious nodes attack mode.