The present work focuses on the surface of Ti6Al4V titanium alloy to improve its microstructure and hydrophilic property using micro-arc oxidation (MAO) in a mixed electrolyte system with different concentrations of calcium salt and phosphate salt. The morphology, the crystalline structure, the thickness and the hydrophilic property of the MAO film were detected by scanning electron microscopy(SEM), X-ray diffraction(XRD), eddy current thickness meter and electrochemical work station. Results show that the MAO film surface is porous and composed of anatase, rutile and a small amount of hydroxyapatite. The amount of hydroxyapatite phase increases with increasing of potassium dihydrogen phosphate concentration. The thickness of MAO film will not change until it increases to a certain value. The ratio of the surface loose zone to the inner compact zone changes with increasing of the potassium dihydrogen phosphate concentration. The thicker loose layer surface is porous and has the hydroxyapatite phase with more Ca and P, which can improve the hydrophilic property and biological compatibility of MAO ceramic film.