Objective To improve the corrosion resistance of AZ31B magnesium alloy. Methods Al coating was sprayed on AZ31B magnesium alloy by using oxygen acetylene. Then scanning electron microscope (SEM) analysis was conducted on Al coating sprayed. The distribution of coating elements was detected by using energy dispersive spectroscopy (EDS). The corrosion resistance of sprayed coating was detected by electrochemical workstation and immersion test; and the hardness was tested by Vickers. Results The combination of the Al coating and the substrate was very good, which presented metallurgical bonding. During the spraying process, sprayed Al coating showed equal axial grain growth. Through the surface scanning element distribution, Mg element was found in the spray coating, which indicated that Mg element had diffused in the substrate. According to the electrochemical workstation, the self-corrosion voltage of Al coating was ?1.45 V, 0.05 V lower than AZ31B magnesium alloy (?1.5 V); the self-corrosion current of Al coating was 1.58×10?4 A/cm2, about 1/5 of AZ31B magnesium alloy (8.66×10?4 A/cm2). The immersion test showed the average corrosion rate of Al coating was about 1/5 of AZ31B magnesium alloy. Conclusion The microstructure and properties of Al coating have been improved.