AZ91D magnesium alloy were used as the materials in this experiment. The directly electroless nickel plating, the stannate conversion processing and the electroless nickel plating on the surface of the magnesium alloys that have formed the stannate chemical conversion film on their surface were researched. The morphologies, anticorrosion ability and the hardness of plating of the magnesium alloys after chemical conversion processing and plating nickel were analysed by scanning electron microscope, salt droplet experiment, microhardness survey etc. The result of the experiment showed that, the conversion film unions with the substrate well, the conversion coating can avoid intense galvanic corrosion after the expiration of the plating, and enhanced the corrosion resistance of the plating. The nickel plating deposited on the conversion coating has high microhardness which could provide good protection for the magnesium alloys.