Abstract: Based on the decoupled analysis of soft-switching resonant process in phase-shift controlled full- bridge power converter, a "1-2-1" cosine mode PWM control waveform is proposed, which is aimed at dealing with the process of power-start and frequently violent dynamic change on welding arc load. According to the generating principle of digital PWM control waveform in DSP, a phase-shift PWM control waveform with "1-2-1" cosine mode is designed, and its control effect is verified experimentally. The results show that, by using this phase-shift PWM mode to control full-bridge power converter, it can not only meet the requirement of effective duty cycle in PWM control pulse with regard to the power output characteristics, but also guarantee the dynamic stability in soft-switching resonant process of leading-leg parallel resonant network and transformer primary side serial resonant network, so that the soft-switching state of power devices will be maintained in the process of power-start and frequently violent dynamic change on welding arc load.