Abstract: Ad hoc Network is a collection of wireless nodes forming a temporary computer communication network without the aid of any established infrastructure or centralized administration. The design of key management schemes and protocols, whose main objective is to provide secure and reliable communication, is one of the most important aspects and basic research filed of secure ad hoc networks. The key management in ad hoc network meets many new challenges due to its intrinsic properties such as multi-hip communication, limited resource and so on. In this paper, a method to improve the random key pre-distribution scheme based on cluster scheme is proposed.The comparison to random key pre-distribution scheme shows that the new approach can substantially improve the connectivity of network and reduce the amount of memory required at the same time.