Abstract: The micro-arc oxidation(MAO) films were prepared on Ti6Al4V in the different concentration of Ca and P electrolyte,then the films went through hydrothermal treatment.The scanning electron microscopy was used to investigate the micro-morphology,Energy dispersion spectrometer and X-ray diffraction were used to analyze composition and phase structure of the coatings.The results show that the contents of Ca and P in the film were influenced directly by their concentration in the electrolyte.The Ca ions were deposited in the coating mostly by diffusion effect,while the P ions enter into the film by electromigration effect.The calcium salts and phosphor salts of the MAO film were transformed to Hydroxyapatite with biological activity after hydrothermal treatment,but the grains of hydroxyapatite would be thick if the treatment temperature was overtopped.The suitable hydrothermal treatment technology is 200℃ and 12H.