Abstract: The oxide layer is produced on weld position by low current assisting arc with Ar+O2 as shield gas in AATIG welding,the oxygen is introduced as active element to change the fluid flow form in the weld pool so that the weld penetration increases.In this experiment,by monitoring the oxygen flow in shield gas of assisting arc to change the thickness of oxidation layer,the different thickness of oxide layers were analyzed by EPMA and XRD respectively,and then calculated through thermodynamics.The result shows that pre-melting oxide layer mainly contains Cr,Mn,Si and their oxide-based composite oxide.With the role of arc force,the oxides in arc center are driven to the arc edge region.Finally,the thickness of the oxide layer in the central region is less than that in the edge.The average oxygen content in the oxide layer by XRD analysis is similar to that calculated through thermodynamics.