Abstract: The mechanism of aging effect on wear resistance of GCr15 bearing steel implanted with nitrogen ions 12 years ago was studied. The test results show that there exists an aging effect of the modified materials by ion implantation. AES and X ray diffraction analyses show that the aging effect of modified materials is due to the multicomponent exchange of the mixed atoms and oxygen atoms adsorbed on the surface of the materials as well as the formation of hard phase.