Abstract: According to the characteristics of short circuit transfer of CO₂ gas metal arc welding, a novel full digital waveform control scheme called quasi-constant voltage control is presented for inverter type arc welding power based on DSP.Short circuit and arc ignition process are not judged according to the output voltage and transfer process between them is smooth.The strategy is also applied to all welding conditions.Initial current at the instant of shortcircuit is suppressed to reduce spatter generation.A triple closed loop control model including real time energy compensation for the arc state based on instantaneous voltage and current feedback control is established.Flexibility and reliability of the proposed fully digitalized soft-switching control strategy is validated by experimental results of 400 A welding machine.The experimental results show that proposed digital waveform control scheme is applicable for different wire feeding speed conditions, and the welding process is stable and the welding bead appearance is good.