Al coating, which has similar properties to droplet metal and metallurgical bonding with the substrate, was prepared on AZ91 alloy surface by droplet coating treatment. The microstructure, phase structure and composition of the area near the coating interface were analyzed. The microhardness and corrosion resistance of the coating were also tested. The results show that the element diffusion takes place between Mg and Al during the droplet coating process, but the process of mixing Mg-rich and Al-rich liquids is limited within a thin layer. The composition, microhardness and corrosion resistance of the prepared coating are similar to those of droplet metal Al. The results demonstrate that droplet coating which can prepare the composition-controllable coating is a promising way for magnesium surface protection by the available corrosion resistant materials.