The application discloses a backup power automatic switching device. The backup power automatic switching device comprises: an alternating-current collection assembly, which is used for carrying out conversion on a collected current signal and a collected voltage signal of a field switch according to the proportion so as to obtain a current input signal and a voltage input signal that can be identified by a microprocessor assembly; an open-into assembly, which is used for obtaining a switch operation parameter that is obtained by conversion of a collected operation parameter of the field switch and can be identified by the microprocessor assembly; and the microprocessor assembly, which is used for generating switching control information according to the current input signal, the voltage input signal, and the switch operation parameter; and an open-out assembly, which is used for controlling changing of an on-off state of the field switch according to the switching control information and switching the state of a primary power source into a work state when the primary power source is back to normal. With the device, the problem that the backup power automatic switching is not accurate can be solved; and effects of accurate, non-flash, and rapid backup power automatic switching as well as comprehensive functions are realized.