The underground combined transformer is a compact combined power distribution facility that installs transformers, high-voltage load switches and protective fuses in the fuel tank. The underground combined transformer is placed in the pit when installed, and has the characteristics of not occupying surface space, being immersed in water for a certain period of time, and being maintenance-free. Due to the above characteristics, it has been widely used in North America. Due to the large population and large urban population density in our country, the use of underground combined transformers is of great significance for saving the floor area of urban power distribution facilities and improving the utilization rate of urban land. Therefore, it has wide application value in urban network transformation and construction.