Considering the problem of time synchronization in dynamic topology under mobile Ad Hoc network, an adaptive time synchronization algorithm is proposed. By using the synchronization method based on the sending and receiving mode, the time delay table between nodes is established, and the time stamp in the flood time synchronization protocol is fitted by local weighted linear regression. Then, the time fitting curve and the dynamic delay table of nodes are analyzed jointly in order to synchronize the time. The simulation results show that the algorithm reduces the average number of packets by about 30% and the clock synchronization precision is increased by about 26% compared with the traditional synchronization algorithm.