Abstract: For its excellent mechanical properties and biodegradability, magnesium alloy has a broad application prospect in medical fields such as cardiovascular stent and bone grafting. However, the corrosion rate of magnesium alloy is too fast to meet the medical requirements of implants. Therefore, a surface modification method was proposed, that is, continuous hammering +annealing treatment were used to nanoize the surface of AZ91D magnesium alloy to improve its corrosion resistance. The X-ray diffraction patterns of magnesium alloy before and after hammering annealing were analyzed, and the grain size was calculate by using Xie Le formula. After that, the electrochemical corrosion behavior of magnesium alloy before and after hammering annealing was studied by electrochemical synthesis tester. The surface corrosion morphology and polarization curve were analyzed. The results show that the surface grain of magnesium alloy after hammering annealing has reached nanometer size. The corrosion resistance of magnesium alloy is significantly enhanced after hammering annealing.