Undervoltage protection device and method of servo motor

The embodiment of the invention discloses an undervoltage protection device and method of a servo motor. The device comprises a voltage conditioning unit and a DSP unit, wherein the voltage conditioning unit internally comprises an amplitude limiting device through which the voltage conditioning unit converts an input alternating current voltage into a direct current binary voltage, the DSP unit comprises a duty ratio calculation subunit and a delay subunit, the duty ratio calculation subunit is used for calculating the duty ratio of the input direct current binary voltage, and the delay subunit is used for calculating alarming time through timing. The undervoltage protection device and method of a servo motor, provided by the embodiment of the invention, have the advantages of ensuring the safe running of the servo motor and taking good use of the overload capability of the servo motor.