The temperature distribution along the thickness direction of AZ31B Mg alloy was measured during rolling with heated rolls, based on the previous study of temperature rise effect during rolling with cold (RT) rolls. The effects of different rolling conditions on temperature distribution and its relation with microstructure were investigated. On this basis, simplified energy-based state equations were established to predict temperature rises. The results show that the two temperature rises of metal layers in different thickness both increase with either increased reduction or decreased initial rolling temperature. The roll temperature has obvious effects on surface temperature and overall temperature rise. As a result, the amount of twin in surface layer decreases sharply and the overall recrystallization zone increases during rolling with heated roll, compared with those with cold rolls. The calculated results by energy-based state equations are in good agreement with the experimental ones.