Abstract: A method and a system provide fast switching between multiple backup power supplies. The method includes building, on the basis of the changing characteristics of the amplitude difference and phase angle difference of a bus voltage, an acceleration model for the changing speed thereof. An optimum backup power supply is selected from the multiple backup power supplies by way of forecasting the changed value thereof. A load on the bus is switched to the optimum backup power supply. The system contains a detecting module, a calculating module, a comparison module, a backup power supply determining module, and a switching module. The method and system are able to ensure the reliable and optimized fast switching of the load on a bus.