It was found that a homogeneous and porous titania layer containing Ca and P was formed and converted into a duplex oxidation layer with hydroxyapatite crystallography by the micro arc oxidation of titanium in calcium phosphate electrolyte. The layer morphology and phase composition were not significantly changed by the Ca concentration. Only the concentration of Ca2+ions in solution, the related Ca and P content and the Ca/P atom ratio in the layer increase with increase of Ca concentration in the lower concentration of Ca. It was noted that the HA crystal morphology, the phase ratio and the Ca/P ratio vary with the hydrothermal temperature and Ca concentration of the electrolyte. The HA crystals can be fined by shortening the hydrothermal time. The above results contribute to the optimization of the composition and morphology of the TiO2/hydroxyapatite composite layer on biomedical titanium.