Abstract: The formation process of molten droplet in shorting- circuit CO₂ arc welding and the influence of welding current on the molten droplet shape and short-circuiting transfer course were analyzed. After the welding current signals acquiring during the welding process being pretreated, an welding wire melting model for waveform controlled short-circuiting transfer welding was established by using the Least Square Method.Based on this model, an experimental research was carried out for the molten droplet size control by adjusting the width of welding pulse current in the initial phase of arc ignition to control the arc energy.The experimental results show that the molten droplet size increases monotonously as increasing the width of pulse current of arc ignition, which means that the arc energy and molten droplet size can be controlled effectively by changing the width of pulse current of arc ignition.