Researches on bending property of the AZ31B magnesium alloy sheet have been focusing on the loading methods and their own performance, while the temperature is less concerned in the past. In this paper, the law of the springback with the temperature changing was especially studied. In addition, the forming characteristics of the microstructure at various temperatures were researched. The experimental results indicated a nearly linear relationship existing between temperature and springback owing to the changing characteristics of the microstructure. A formula for calculating the bending springback by temperature of 0.8mm magnesium alloy sheet was obtained, which was according to the data obtained on the basis of physical experiments.