The main and auxiliary switching process involves the large-capacity asynchronous motor used in various systems (such as water pumps, fans, etc.) that are accompanied by strong electrical and mechanical shocks during the restarting or reinput process, especially the influence of the motor group restarting shock. The process includes the dynamic behavior of the electromagnetic and mechanical transient change process. In Order to quantitatively analyze the dynamic behavior of induction motor starting, the general steady-state analysis method can no longer be accurately solved, it is necessary to consider the dynamic load model of the transient process, and select ETAP software to realize the model establishment and transient process simulation calculation. For high-power motor load starting, the motor may fail to start due to low starting torque or other running motors connected to the power grid. Therefore, this paper selects typical high-power motors as the research object as the largest single load, and considers the harsh power supply conditions, and the transient conditions of the above-mentioned plant power switch motor group start, To verify whether the motor starting or restart will cause itself and other motors to stall, or whether it causes the EDG diesel generator to start. Whether the power system of nuclear power plant can resume stable operation after the above transient process has become an important index for evaluating the power system design of nuclear power plant. In this paper, the simulation study of the switching between the main power supply and the auxiliary power supply of the nuclear power plant, and the starting process of the high-power motor is established, the power system model of the power grid is analyzed at high voltage and low voltage, and the transformer is automatically loaded. The on-load voltage regulation, the plant power switching process and the high-power motor starting simulation calculation, effectively reduce the cost of the experiment, Has great economic benefits, it has positive significance for fault analysis.