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In order to study the effect of pre - oxidation treatment on the quality of the nitriding layer of stainless steel parts, quenched and tempered samples were treated with different pre - oxidation and sand blowing treatments before nitriding. The color of the preoxidized film was observed visually. The microstructure, depth, hardness, and brittleness of nitriding layer were measured by metallographic microscope and hardness tester. Results showed that the passivation film on the surface of 1Cr11Ni2W2MoV stainless steel could be destroyed if the steel was preoxidized at 550 ℃ for 5～20 min before nitriding. So the hardness, depth and structure of the nitriding layer could meet the technical requirements for nitriding if treated so. Furthermore, the uniformity and nitriding speed of the layer were better than that of the layer with only sand blowing treatment before nitriding.