The transformer, as an important piece of equipment to maintain voltage stability and improve voltage quality in the power grid, has been a research hotspot in a number of fields. With the development of power electronics technology in recent years, transformers gradually show a trend in power electronics because of the high controllability of power electronics devices compared with traditional mechanical structures and their characteristics of no arcing. This paper divides the development direction of power electronic transformer into two stages, and summarizes the topology of the power transformer electronic process stages. On this basis, the impact of each power transformer at an electronic stage on on-load voltage regulating is introduced in detail. Finally, the influences of power transformers at different electronic stages on voltage stability are contrasted, and the development trend and the key problems of the transformer are summarized and prospected. This work is supported by National Natural Science Foundation of China (No. 51507029).