An anodic oxidation film is fabricated on AZ91D magnesium alloy by the simple DC anodic oxidation. The adhesion of the Mg-rich primer on AZ91D substrate was dramatically increased by the anodic oxidation film. The anodic oxidation film/Mg-rich coating system impedes the electrolyte permeation to the substrate and hinders the expansion of corrosion area on the substrate. The anodic oxidation film yields a significant increase in the lifetime of the anodic oxidation film/Mg-rich coating system.