The curves of true stress-strain of AZ80 Magnesium alloy had been tested with thermal simulation experiment, at the conditions of the experimental temperature being 260℃~ 410℃, and strain-rate being 0.001~ 10s-1, and the deformation degree being 50%. According the Arrhenius equation, a kind of constitutive equation of AZ80 Magnesium alloy which considered the strain had been put forward, and the relative errors between calculation results by the stress-strain model and experiment results are less than 10.5%.