Abstract: Node cooperation mechanism is given out, which is based on the value of price divided utility. The mechanism constructs the directed graph that weighted of that value, and based on the graph, the mechanism uses the Dijkstra algorithm to receive the trusted path. At the same time,the network delay is vitally taken into consideration. As a result, the mechanism finds the best path of delay time which is much shorter than before, and the total value of the price divide utility of the path is significantly much smaller than the others.In the end,the best path is developed to transmit messages in opportunistic network. Simulation results show that the mechanism can resists the greedy behavior of selfish nodes to a certain extent, and it is also useful to efficiently promote the cooperation between the nodes, meanwhile, it helps to improve the performance of the network.