A wireless sensor network is a network composed of a large number of sensor devices deployed in a wireless environment. The cooperative operation between wireless nodes requires the network nodes to maintain a common time. The time synchronization is a wireless sensor network supporting technology,and the traditional classification method cannot effectively reflect the characteristics of time synchronization algorithm. The existing time synchronization algorithm is reclassified from the perspective of whether there is feedback in the information exchange. At the same time,the progress of the time synchronization algorithm is described in detail. The new classification method can effectively reflect the characteristics of synchronization precision and synchronization energy consumption of the algorithm. The feedback time synchronization mechanism is higher than the non-feedback time synchronization mechanism in synchronization accuracy and synchronization energy consumption. Finally,the shortcomings of the existing time synchronization algorithm are summarized and the future development direction of time synchronization technology is prospected.