AZ80 magnesium alloys were deformed at 200, 250, 300, 350 and 400 ℃ with different deformation degree of 50%, 75%, 83%, 87% and 90%, respectively. The corrosion properties of different deformed AZ80 samples were studied by galvanic test in 3.5% NaCl solution. The results show that plastic deformation could improve the corrosion resistance of AZ80 alloy; and the corrosion rate of AZ80 deformed at 250 ℃ with the deformation degree of 83% was the lowest, which was 33% of the as-cast AZ80 alloy. Further studies of the microstructure show that the refined grain size and continuously distribution of β phase around the grain boundary did have a positive effect on the improvement of corrosion resistance of AZ80 alloys. For AZ80 alloys, the smaller the grain size is, the more homogeneous the structure is, and the better the corrosion resistance is.