Abstract: Adding active gas in inert shielding gas may control the shape of molten pool effectively, which also makes regulating the contents of oxygen in molten pool easilier. This work reviewed the effect on the shape of molten pool by adding O2 and CO2 respectively in He and Ar shielding gas, and summarized the optimization of additive amount for active gas. This work also discussed shape change degree of welded molten pool under dif-ferent welding processes,which is essentially helpful to give guidance in optimizing production process.