Abstract: Developing more efficient welding methods and processes is a hot topic in the international welding industry, and increasing welding current and extension length is a direct approach to improve melting efficiency of MAG welding. Through improving commercial MAG welding machine, wire feeding speed can reaches 50 m/min, and the welding current is up to 500 A or more so as to further enhance welding efficiency. But the formation of rotating spray transfer of droplet, resulting in welding arc instability and lots of spatters, thus an alternating magnetic field is applied to control the arc morphology and droplet transfer behavior. With the welding experiment, the influence of welding current on spatter rate and metal evaporation rate was analyzed and the droplet transfer behavior and weld appearance under alternating magnetic field was studied. The results show that under high welding current with low frequency magnetic field can effectively enhance the arc stiffness and stability, shorten the length of liquid stream and reduce the deflection of fluid tip, improve the weld appearance, and then greatly increase the welding efficiency.