Since 2016, Some nuclear power plants in the northern region has been facing severe situation due to seasonal heating; and because of seasonal hydropower generation, the generation situation of some nuclear power plants in the southern region is more serious. At present, the power supply in the production preparation area of most nuclear plants is mostly purchased electricity. There is a big difference between the price of electricity purchased from external power grid and the cost of power generation from nuclear plant. Therefore, if the production preparation area of the nuclear power plant power consumption is changed to power supply by itself (Auxiliary power), it will make a great contribution to energy saving and power saving, cost reduction and efficiency promotion. There is no study on the efficiency promotion of nuclear power generating units at home. This study mainly focuses on the project of power supply migration in production preparation area of nuclear power plant. This study is carried out from four aspects: transformer capacity, bus voltage drop of 6.6kV, capacitive current, and economy. The definition of production preparation area of nuclear power plant: the living area of the on-duty dormitory of the plant, administrative office area and other relevant areas.