The present invention provides a switch power circuit with a backup battery for power supply, comprising an input rectifier module, an PWM switch control module, a transformer module, an output rectifier diode, a negative feedback module, a backup battery, an isolation diode unit and a zener diode; the anode of the output rectifier diode is connected with the positive output end of the transformer unit, the cathode of the output rectifier diode is connected with the cathode of the isolation diode unit, the anode of the isolation diode unit is connected with the anode of the backup battery, the cathode of the backup battery is connected with the negative output end of the transformer module; the cathode of the zener diode is connected between the cathode of the isolation diode unit and the cathode of the output rectifier diode; one end of the negative feedback module is connected with the anode of the zener diode, and the other end of the negative feedback module is connected with the control port of the PWM switch control module. The present invention has beneficial effects of reducing output consumption of switch power supply and increasing conversion efficiency of switch power supply.