Micro-arc oxidation films were prepared on magnesium alloy AZ91D in a aluminate electrolyte. The effects of electric parameters during the micro-arc oxidation process on properties of MAO films were systematically investigated using the Taguchi experimental analysis method. The optimized parameters are 180 V voltage, 30 min oxidation time,50 Hz frequency,30% duty cycle. The corrosion resistance of the MAO film was examined by means of AC impedance.The results show that the resistance of MAO film treated on optimized conditions increase by two orders compared with the magnesium alloy substrate. This enhances the corrosion resistance of the magnesium alloy.