As one of the key technologies in ad hoc networks, clock synchronization is fundamental to slot assignment, multiple access strategy, data aggregation and so on. In order to decrease the complexity and iteration times of popular distributed clock synchronization algorithms for ad hoc networks, a new method using 2-hop neighbors' time information is proposed. The frame starting time of each node is updated by using a simple local rule based on the average of its own frame starting time plus its 1-hop and 2-hop neighbors'. Finally, all nodes have the same frame starting time and the synchronization of ad hoc networks is achieved. The simulation results indicate that iteration times of clock synchronization has decreased by 78% by using method in this paper compared with the other which uses only 1-hop neighbors' time information.