The work aims to improve the corrosion resistance of magnesium alloys. Aluminum coating was prepared on AZ31 magnesium alloy surface by constant current deposition. The micro-morphology and corrosion morphology of the coating were observed by optical microscopy and scanning electron microscopy. The effect of deposition time on corrosion resistance of Al-coated magnesium alloys was investigated by open-circuit potential and potentiodynamic scanning. Aluminum coating was successfully prepared on AZ31 magnesium alloy by constant current electrodeposition. The corrosion potential of the uncoated AZ31 magnesium alloy was negative and about -1.68 V by electrochemical corrosion test, and the corrosion current was the largest. When the deposition time was 1 h, corrosion potential of magnesium alloys shifted positively and was about -1.34 V. The corrosion resistance of magnesium alloys was improved, but the corrosion current decreased slightly. When the deposition time was 2 h, the sheet aluminum grew into granular particles, the corrosion potential was about –1.32 V, and the corrosion current was obviously reduced. With the prolongation of deposition time, the coating continued to grow and the granular Al began to diffuse to the suitable growth position. When the deposition time was 3 h, a lamellar Al diffusion zone was formed on the surface of magnesium alloy, and the corrosion potential was more positive and about –1.30 V. At the same time, the corrosion current reached the minimum. Aluminum coating can be successfully prepared on AZ31 magnesium alloy by constant current electrodeposition and can effectively improve the corrosion resistance of magnesium alloy. When deposition time is 1 h, the corrosion resistance of magnesium alloy is slightly improved. When deposition time is 2 h, the corrosion resistance of magnesium alloy is further improved. When deposition time is 3 h, the aluminum coating can provide the best protection effects for magnesium alloy, the corrosion is the most weak and the corrosion resistance of magnesium alloy is improved obviously.