Sensibility and protective design of single event transient effect for Pulse Width Modulator(PWM) was validated by pulse laser. During test, by changing the energy of the pulse laser and scanning the PWM circuit step by step, the energy threshold of the pulse laser and the sensitive region of PWM induced single event transient effect were determined. By changing the soft start configuration circuit design of PWM, the rationality of the protection circuit design was verified, which provided a technical reference for the single event transient protection design of satellite power subsystems.