Abstract: Nitrogen implantation in Cr12MoV steel was performed by plasma source ion implantation(PSII) technique.The composition and microstructure of the implanted layer were analyzed by Auger electron spectroscopy and transmission electron microscopy.The results show that the distribution of the nitrogen concentration in the implanted layer has the characteristic like Gauss and that the martensite structure is fined and an amorphous structure forms in the implanted layer.Relative tests revealed that the microhardness and friction properties are improved obviously.