A robust trust model based on group for P2P environments-RobustGroup is put forward, which measures trust values based on the group relationship between requesting peers and serving peers. Trust’s aging time and peers’ similarity are introduced with weights for direct trust and indirect trust being dynamically adjusted in trust calculation against critical issues affecting trust evaluation such as false feedback, incentive and penalty, Whitewashing behavior, dynamic trust. Simultaneously service control policies are implemented on the basis of groups, and peers’ initial trust is determined by behavior in “silent time”. The simulation shows that the proposed model has advantages in successful requests and system overhead over the existing P2P trust models.