Due to the rapid development of power electronics and new energy generation, conventional transformers cannot meet the higher requirements of intelligent grids due to a lack of controllability. While solid-state transformers (SSTs) are currently costly, making it impossible for them to be used widely in power networks. For this reason, a compromise solution of a hybrid transformer (HT) combining the traditional line frequency transformer (LFT) with power electronic devices has attracted more and more attention. Based on existing HT research, topologies of HT are classified according to installation position and connection type of power electronic devices. Rough theoretical analyses were carried out from the point of view of voltage compensation, current compensation, and power flow control. A review of HT topology in recent years is also included.