Mo ions extracted from a metal vapor vacuum arc ion source (MEVVA) were implanted into 4Cr5MoV1Si(H13) steel samples with a high implantation dose of 5×1017cm-2 and a pulsed ion beam flux of about 300 μA·cm-2·An optical interference microscope and pin-on-disc apparatus were used to investigate the wear and friction characteristics of the steel. The results from Rutherford backscattering spectroscopy (RBS) and the collision theory demonstrated that the radiation enhanced diffusion gave great influence on the Mo profile. It was observed by X-ray photoelectron spectroscopy (XPS) and grazing-angle X-ray diffraction (GXRD) that carbide of Mo appeared in the doped region for the implantation at 48 kV. The results showed that improvement in the wear resistance of the Mo-implanted steel were mainly due to the formation of Mo2C in the doped zone and the implantation affected zone underneath. Oxidation resistance of the surface iron and the surface with small crystal grains gave influences on the wear resistance in a way. Mo ions extracted from a metal vapor vacuum arc ion source (MEVVA) were implanted into 4Cr5MoV1Si (H13) steel samples with a high implantation dose of 5 × 10 17 cm -2 and a pulsed ion beam flux of about 300 μA · cm -2 An optical interference microscope and pin-on-disc apparatus were used to investigate the wear and friction characteristics of the steel. The results from Rutherford backscattering spectroscopy (RBS) and the collision theory prototype that the radiation enhanced diffusion gave great influence on the Mo profile. It was observed by X-ray photoelectron spectroscopy (XPS) and grazing-angle X-ray diffraction (GXRD) that carbide of Mo was in the doped region for the implantation at 48 kV. The results showed that improvement in the wear resistance of the Mo-implanted steel were mainly due to the formation of Mo2C in the doped zone and the implantation affected zone underneath. Oxidation resistance of the surface iron and the surface with small crystal grains gave infl uences on the wear resistance in a way.