Abstract: In order to improve the edge effect in the process of ion carbonitriding (PNC), the uniformity and corrosion resistance of 316L steel were studied under the same process conditions of conventional ion carbonitriding (R-PNC), the sample was carbonitriding under partial covered (PC-PNC) and the sample was carbonitriding under complete covered(CC-PNC).Optical microscope (OM), atomic force microscope (AFM) and CHI660E electrochemical workstation testing machine were used to characterize the structure and corrosion resistance of the diffusion layer.The results show that the edge effect of the diffusion layer is obvious in R-PNC, and there is no diffusion layer in the center of the sample, and the corrosion resistance is poor.Under PC-PNC, the uniformity and corrosion resistance of the diffusion layer are improved, but there is still no diffusion layer point in the center of the sample.CC-PNC significantly increases the diffusion layer thickness of the sample, the edge effect basically disappears, and the corrosion resistance is sharply improved compared with that of PNC and PC-PNC.The shielding method can change the electric field distribution, ion motion direction and ion energy of the sample surface during the carbonitriding process, so as to improve the edge effect.The nitriding effect is good when the distance between the shielding plate and the carbonitriding surface is 8-10 mm, the optimum shielding spacing is 8 mm, and the optimized technology has been applied in production.