Abstract: In grid environment, grid nodes provide services with QoS guarantee, so how to choose a credible service is a critical problem. It is proposed that basic probability assignment be constructed based on the QoS constraints that the services provide, and that in the process of building the basic probability assignment, a partial relation is inducted in order to remove the worthless history information. And referring to the behavior of human society the reputation model of the grid nodes is established. Moreover, based on the discounting operator and the consensus cooperator, the reputation options from different grid nodes can be integrated. In order to avoid the overload in some nodes, a balancing scheme implemented with a biased roulette wheel is adopted. Simulation tests prove that the model can tackle the trust problem in a simple and efficient way.