A hardened layer possessing good bonding strength with substrate was prepared on the surface of TC4 titanium alloy by a process of vacuum pulse oxidation. The microstructure, hardness and brittleness of hardening layer were analyzed.The results show the hardened layer comprises a surface oxide layer and an oxygen diffusion zone, TiO₂of the oxide layer happen to change, oxygen penetrate into the substrate, the phase of oxide layer is composed of 琢-Ti, rutile TiO₂, TiO and Ti₃Al, surface microstructure appear compact,the surface hardness of the TC4 titanium are 650 ~ 670 HV, the thickness of the hardened layer can reach 60 ~ 80 μm, because of the effect of solid solution strengthening in oxygen diffusion zone, the hardened layer has low brittleness and the hardness gradient of hardened zone is flat .