In order to study the effect of calcium concentration in the micro-arc oxidation electrolyte on the surface structure of porous titania coatings by compound oxidation process (pre-oxidation and micro-arc anodic oxidation), X-ray diffusion and the scanning electronic microscopy equipped with EDS were used to analyze the morphologies, phase structures, element compositions of the coatings. An image analysis software was employed to calculate the porous ratio to the surface area. The results show that the coatings formed by the compound process were all composed of titanium, anatase and rutile. The calcium concentration has certain effect on the surface structure. With the increase of calcium concentration, relative amount of the anatase reduces and the rutile increases; The content of calcium and phosphorus in the coatings decreases and the atomic ratio of Ca/P rises. Variation of the calcium concentration has no remarkable influence on the surface porous ratio of the coatings in the selected phosphate concentrations.