The security issues in mobile Ad hoc network, especially caused by inner malicious nodes are analyzed. By tracking the behavior of nodes, trust level of each node can be evaluated and managed; then actions of malicious nodes will be constrained and the security and reliability of entire network are enhanced. According to the features of Ad hoc. The scheme proposed in not only extends the conception of trust but also include the trust computation model and trust management mechanism. Simulation experiments show the novel scheme is more efficient than other trust schemes in traditional protocols.