Abstract: A great deal of malicious behaviors makes it hard to support validity and availability in the mobile P2P networks.Most of current peer-to-peer trust models are applicable to fixed network，neglect the effect of different terminals，and could not promise the trust computation of different domains.This paper presents a trust mechanism，Multiple Granularity Trust Model（MGT），which imports the clustering and time factor，then gives the implementation of the MGT source selection protocol.Emulating experiment shows that MGT is more effective on protecting the network from many malicious behaviors and more robust on trust security problems.