The cast magnesium alloy AZ31B cylindrical samples of high temperature compression tests were taken under the deformation temperature 250-450℃and strain rate 0.005-5 using Gleeble-1500D thermal/mechanical simulation testing machine. Based on the high precision flow stress models and the rigid-plastic finite element analysis software, numerical analysis of coupled thermal-stress of hot rolling process under different initial rolling temperatures, different rolling reductions and different rolling speeds was carried on. Under different conditions, models of temperature field of magnesium plate deformation region were established by using mathematical analysis methods. The results showed that, under different conditions of hot rolling processes and rolling zone, regional distribution of rolling deformation temperature was so different that mathematical models of temperature field should be divided into different process conditions to establish. The mechanism of temperature controlled online was more simple by using mathematical equations to characterize the magnesium alloy heat transfer process ,and heat transfer mechanism of magnesium plate rolling in wide ranges was accurately characterized.