Firstly, the working principle of fast-switching device is summarized. From four aspects of fast synchronous switching, synchronous capture switching, residual voltage switching and long-delay switching, the basic types of fast-switching device are analyzed. On this basis, the application countermeasures of fast-switching device in multi-power supply system are put forward. The purpose of the research is to improve the operation efficiency of multi-power supply system and to help enterprises develop in the long run.