Abstract： A microstructural evolution model was integrated with a thermalmechanical elasticplastic finite element method to quantitatively simulate the hot deformation and microstructural evolution of magnesium alloy AZ31B at two different compressive modes, constant strain rate and constant die velocity. The stressstrain curves and recrystallized grain sizes were obtained from hot compressive deformation of AZ31B on Gleeble1500 thermosimulation machine and integrated with the finite element model through the user subroutine interface. It is shown that the fields of deformation and microstructure are nonuniformly distributed as a result of the existence of friction. Compared with the sample compressed at a constant strain rate, the mean value of the grain size decreases and the mean square error increases slightly for the sample at a constant die velocity.