In wireless mesh networks, the sample space of evidence may be not integrative or reliable because of the change of network topology and the occurrence of wireless collision. It makes the existing trust evaluation models inapplicable. To evaluate trust values of nodes and establish trust relationship in nodes, a trust model is proposed on the basis of the analyses of the existing trust models and the minimal principle of uncertainty metric. The model reduces the influence of the non-integrated and unreliable sample space through importing a credible parameter. According to the real situation of networks, the model can minimize the amendment of evaluation values in the whole scope. Contrasted with the evidence-based trust model, the simulation results show that the proposed model is effective.