Abstract: Taking the 20Cr2Ni3 finished piercing plug and the failure piercing plug as the research subjects,the effect by Ni on piercing plug being prepared and operated are studied. And the morphology and chemical composition of the oxide film of the plug are analyzed. It is identified via the research that when the said porous finished piercing plug with a 2-layer oxide film structure fails after piercing operation,most part of the outer oxide film peels off,while the inner oxide film sticks onto the basal body tightly;and that during the plug preparation and piercing process,Nitrogen(Ni)always exists in the form of elementary substance in the inner oxide film. The analysis leads to such a conclusion that during the high temperature piercing process,at the Ni-enriched location of the oxide film,the structure is dense and free of any crack,whereas at the Ni-poor location of the oxide film,big cracks are developed;and that in this case Ni acts as some kind of binder,and gets the oxides bond closely,which protects the plug so well.