Abstract: SiO₂(Mg) coating was applied on the surface of AZ31 magnesium alloy by mechanical alloying. The microstructure and microhardness of the surface coating were analyzed by XRD, microhardness tester and scanning electron microscope. The corrosion resistance of AZ31 magnesium alloy before and after being coated was tested by electrochemical workstation. The results showed that SiO₂ was successfully coated on the surface of AZ31 magnesium alloy. At the same time, with the increase of milling time and ball-to-material ratio, the microhardness increased, which could be up to 370.6 HV, 15.2% higher than that of the substrate. The thickness of the coating also showed a trend of increasing first and then stabilizing. However, if the ball milling time was too long, cracks would appear in the coating. When the ball-to-material ratio was 15:1 and the ball milling time was 15 h, the thickness of the prepared coating was 148 μm, the coating compact and the bond between the film and substrate excellent. The corresponding self-corrosion current density was reduced by 1 magnitude and the corresponding corrosion current increased by 6.5% compared with those of the substrate. The corrosion resistance was obviously improved.