The invention provides output stabilization system and method of a welder. The system comprises an input detection unit, a comparison unit, a compensation unit and a control unit, wherein the input end of the input detection unit is connected to an alternating current power supply source, and the input detection unit outputs a detection result of the power supply source; the comparison unit is connected to the input detection unit and a power supply source standard value and is used for comparing the detection result of the power supply source with the power supply source standard value and generating a comparison result; the compensation unit is connected to the comparison unit and is used for generating compensation signals based on the comparison result; and the control unit is connected to the compensation unit and the alternating current power supply source and is used for superposing the compensation signals and the alternating current power supply source and generating a stable welder work power supply. By adopting the system and the method, the work voltage of the welder from the alternating current power supply source can be stabilized, and fluctuation of the alternating current power supply voltage is compensated by regulating PWM (Pulse Width Modulation) duty cycle, thereby efficiently avoiding poor welding caused by unstable voltage of commercial power.