Abstract: The stress-strain curves of AZ80 magnesium alloy are tested by thermal simulation experiment, which the deformation temperature is from 533K to 683K, and strain-rate is from 0.001 to 10 s-1, and deformation degree is 50％. The grain size of dynamic recrystallization (DRX) increases with rising of deformation temperature and reducing of strain-rate. According to the Arrhenius equation and experiment data, the energy of thermal activation of AZ80 magnesium alloy is determined, and a kind of constitutive equation of AZ80 magnesium alloy is established. According to the Sellars equation, the dynamics model of AZ80 magnesium alloy is established, which is defined as the relationship between the volume fraction of DRX and deformation temperature and strain-rate. The kinematics model of AZ80 magnesium alloy is established, which is defined as the relationship between grain size of DRX and deformation temperature and strain-rate. The calculated results of grain size of DRX are in agreement with that of experiment, and relative errors are less than 11.8%. The relationship model between critical strain and steady strain of DRX with deformation temperature and strain-rate are established.