The density Al coatings were prepared on AZ91 D magnesium alloys by low temperature high velocity oxygen fuel ( LT-HVOF) , and which was post-treatment by micro-arc oxidation, then the Al / Al₂O₃composite coatings were acquired.And the film forming process, microstructure and composite, corrosion resistance of the oxidation film, were analyzed by SEM,XRD and Neutral Salt Spray Test ( NSST) and contrasted with the MAO films of the 2024 aluminium alloys and AZ91 D magnesium alloys. As a result, the morphology of the MAO film on Al coatings is porous and coral like with no micro-crack,and its MAO process is the same like 2024 Al alloy ’s. And the main phase composition of the MAO films on the Mg / Al composition coatings is γ-Al₂O₃. The MAO films on the Al coatings have excellent corrosion resistance of artificial seawater and which could markedly improve the anti-corrosion property of the magnesium alloys.