Magnesium alloy is a lightweight structural material, but commercial AZ31B magnesium alloy has poor wear and corrosion resistance. WC-12Co has high hardness, wear resistance and corrosion resistance. In this paper, WC-12Co coating was prepared on AZ31B substrate by high velocity oxygen fuel (HVOF) spraying technology to improve its comprehensive service performance. Based on the surface of AZ31B magnesium alloy substrate with different roughness, the coating microcharacterization experiment was carried out. The effects of substrate surface roughness on the hardness, adhesion, wear resistance and corrosion resistance of the coating were revealed. The results show that the adhesion between the coating and the substrate and the corrosion resistance of the coating are significantly improved with the increasing surface roughness.