Abstract: By analyzing the security problem of the hierarchical mobile Ad Hoc networks, a security clustering algorithm based on reputation (SCAR) is presented. In the algorithm, the nodes' reputation is acquired through monitoring the network behaviors by neighboring nodes so as to improve the security of the clustered architecture. The mechanism of reputation exchange between nodes increases the accuracy of reputation evaluation, and the stability of clusters is ensured by the two evaluation indices, i.e., correlation and relative mobility. The weight of each node is computed according to the demand for communication and running condition of networks, with the reputation correlation and relative mobility mentioned above considered comprehensively. Then, the clustered architectures are built, maintained and updated by modul weights to strengthen the security supervision of the cluster head and gateway. Simulation results showed that the proposed algorithm improves the system security and stability.