Under a wide range of deformation conditions, hot compression tests of AZ31B magnesium alloy cast cylinder were carried by Gleeble-1500D thermal simulator. According to the strain softening characteristics of magnesium alloy, a new thermal deformation constitutive model was established. Relying on Deform-3D, the coupled thermal-stress simulation of hot rolling process of magnesium plate was analyzed. Based on the rolling theoretical assumptions, macroscopic continuum mechanics and thermodynamics, strain and strain rate value distribution models, three-dimensional temperature field and stress field mathematical models in rolling deformation zone were established by mathematical analysis method. The results showed that the new thermal constitutive model was in a higher accuracy and the average relative error was 5.1%.Strain distribution model, strain rate value distribution model, mathematical model of temperature field and mathematical model of stress field were not only concise in form and easy to be controlled online, but also could accurately characterize thermal-mechanical coupled deformation mechanism of hot rolling of magnesium plate.