Two different micro-arc oxidation films were prepared by blasting and polishing pretreatment before micro-arc oxidation. The morphology, chemical composition and corrosion resistance of the two films were compared, the effect of pretreatment on voltage value of micro-arc oxidation was analyzed. The results show that: the polishing samples of voltage value in the oxidation process are higher than the sandblasted specimens; The corrosion resistance of micro-arc oxidation coatings is greatly improved compared with substrate, and the corrosion resistance of polishing oxidefilm improves about 40% compare for blasting oxide film; The surface morphology of blasting oxide film retaines the rough topography of the sample blasting, while the polishing oxide film surface is smoother, the size of holes are smaller and more and uniform distribution compared with the blasting; The surface composition of oxide film consist of main elements of O,Mg,Si,Al,and have nothing with pretreatment methods.