The temperature change history of AZ3lB Mg alloy was measured under different rolling conditions. An in situ measurement method through inlaid thermocouples was used. The results show the whole temperature variation process consisted of deformation process(0.02~0.08s) and subsequent temperature homogenizing process(0.8~1.2s). The temperature rises in these two stages both increased with either increased reduction or decreased initial rolling temperature. Those two temperature rises reached 80℃ and 35℃, respectively, for 45% rolling at 200℃. On this basis, two empirical formulas were established to predict temperature rises. The deformation induced temperature rise significantly affected the microstructure and recrystallization behavior of rolled sheet.