The invention relates to a time synchronization method. The time synchronization method is applied to a wireless sensor network with discontinuous communication, and comprises the steps of carrying out opportunity synchronization on sensor nodes in the wireless sensor network during each synchronous cycle, and carrying out prediction calibration on the sensor node without being synchronized to correct time after the opportunity synchronization is finished, thus achieving the synchronization. According to the time synchronization method, the nodes of the whole wireless sensor network are synchronized in a mode combining the opportunity synchronization and the prediction calibration without dependence on a specified network topology structure, thereby well adapting to network topology change caused by the moving of the nodes or sleeping schedule, reducing the energy consumption of the nodes, and saving the resources of wireless channels.