Abstract: In P2P networks，it is inevitable to interact between unknown peers for services provided.To reduce risk，it requires the trust evaluation prior to and posterior to interactions.A trust model in time domain is proposed in this paper to characterize the time procedure of reputation.To a peer，the local reputation evaluation should not be determined by the number of success and failure transactions，and the global reputation should pay more attention to itself evaluation as the count of transactions increased.This model can evaluate accurately and dynamically the trust of the given peer，and can prevent the collusion form the recommend peers.