Ce conversion coating was prepared on the surface of AZ91 D magnesium alloy by chemical immersion, cerium conversion treatment process was optimized and the morphology of the cerium conversion coating, organizational structure and corrosion resistance were studied. Epoxy resin and fluorocarbon resin were respectively brushed on the conversion coating, and the mechanical properties of the two composite coating were tested. The results showed that the Ce conversion coating was consisted by two-layer-coatings and conversion processing in the optimization of process conditions is able to improve the resistance of basement to corrosion, the adaptability of Ce conversion coating to epoxy resin was better than to fluorocarbon resin.