Abstract: In low vacuum condition,0Cr18Ni9 stainless steel sheets,with one in supply state and the other pre-oxidized at 800℃ in air,were heated,and the steel sheet in supply state was soaked in molten copper. It was found that the structure of oxide film changed after heating in low vacuum environment,and this film can not prevent the solution of stainless steel by the molten copper. Through investigation into the mechanism of removing oxide film on stainless steel sheet in vacuum condition and thermodynamic calculations,it was proposed that carbon could deoxygenate and weaken the oxide film. Once the molten copper met the stainless steel substrate by flowing through the cracked oxide film,the stainless steel would rapidly dissolve due to the diffusion of Ni atoms into the molten copper,and subsequently the oxide film would float on the molten copper. Finally,the oxide film would be removed under the action of surface tension in low vacuum condition.