In order to solve the problem of voltage drop in the process of mode switching in permanent magnet starting/generating system, a mode switching strategy considering capacitor charging and discharging delay is proposed based on the traditional mode switching strategy. By considering the delay process of capacitor charging and discharging, the control structure and the switching time of electrical load switch are changed to reduce the drop voltage during the switching process. Set the generation mode speed threshold in the mode switching controller, so that it can smoothly switch to the starting mode when the generation mode cannot be maintained. This switching strategy improves the system stability. Through simulation experiment, the correctness and feasibility of the above switching strategy are verified.