Abstract: A novel control strategy of repetitive control and double closed-loop control is presented based on analysis of the merits and demerits of traditional control.Repetitive control uses the repetition trait of interferer, periodically correct output voltage to improve preferably the steady state characteristics of the system, and double closed-loop control uses the current inner-loop to restrain interferer fast to improve preferably the dynamic state characteristics of the system.Based on the analysis of influencing fator of arc welding characteristic, a DSP based whole digital combined control system was established to improve arc welding technics characteristic.During the "short" phase, di/dt and the peak value of current are adjusted properly, and the current of short circuit uses return round outer-drag.During the "arc" phase, the burning-arc voltage stable is kept, and the anew striking arc current is increased.The analysis result shows that by this digital waveform control inverter power source, the welding characteristic can be improved greatly, such as reducing the splash clearly, good appearance of weld and the stability of welding process.