φ（Ar）78%+φ（He）20%+φ（CO2）2% shielded MAG automatic welding was proposed to study the effects of welding parameters by using 16 mm thickness 304 L stainless steels. The results showed that short circuiting transfer can lead to the unstable electric arc and excessive spatter. Besides, porosities were observed in the weld. The stable electric arc can be obtained by using spray transfer, but the helium arc could cause undercut. Finally, the weld quality was satisfactory by using the average current of 240 A.