The work aims to prepare a hard and abrasive hardening layer on the surface of Ti6Al4V titanium alloy. A dense oxygen-diffusing hardening layer was prepared on the surface of Ti6Al4V titanium alloy with pure oxygen working medium gas by taking advantage of vacuum technique. Phase composition of the oxygen-diffusing layer was studied with XRD, oxygen-diffusing layer and grinding crack structure were observed with metallurgical microscope, surface hardness was tested with micro-hardness tester, and wear resistance was analyzed by MM-U10A end-face abrasion tester. TiO2, TiO, Ti3Al and Al2O3 were major phases in the surface layer. The oxygen-diffusing layer was thinner when the Ti6Al4V titanium alloy was oxidized at lower temperature; the layer thickness, hardness and wear resistance increased as the temperature increased; at the temperature of 760 ℃, hardness of the surface exceeded 750HV, over 2.5 times higher than that of the substrate; hardness of the effective hardening layer exceeded 60 μm; weigh loss was only 1/4 that of unoxidized sample; surface friction trace was fine, no surface tearing was observed and the surface oxygen-diffusing layer was intact. The oxide aggregate started to grow and the oxygen-diffusing layer transformed into loose microstructure as the oxidizing temperature further increased. As a result, the hardness and wear resistance decreased. The surface hardness and wear resistance of Ti6Al4V titanium alloy can be significantly improved by vacuum oxidation technique.