Abstract: To study the heating mechanism of the welding wire and the arc shape and stress process during the dreplet tranfer in variable polarity pulsed MIG welding, an experimental platform was established to measure the images of droplet transfer and electrical signal synchronously. To obtain the relationship of current waveform and the shape of droplet, the weld current and droplet transfer were analyzed correspondingly. With the fixed frequency ratio, the effect of time ratio to droplet transfer was obtained by analyzing the driving force of droplet at different current stages. A pulse of a drop of molten drops transfer process was achieved by adjusting the process parameters and then the uniform and stable welding seam was obtained. Studying feature sizes of the molten drops by analyzing the drop off form and the results shows that the electrical signal duration of different bands have obvious effects on droplet size.