Abstract: In the Web service，a new model based on the group’s trust is proposed，to eliminate and control bad behaviors of nodes，and to encourage good behavior of providing reliable services，and to establish an effective credible assurance mechanism.The model takes into account the individualization of node’s experiences and group’s behaviors.The analysis shows that the new model reduces the scale of computing values of global reputation，and improves the efficiency of calculation，and solves sparseness of access in a large-scale distributed network to a certain degree，and possesses some incentive and robustness.