To evaluate the hot flow behavior of homogenized AZ80 magnesium alloy containing 0.8 wt% yttrium, isothermal hot compression tests are conducted among the different temperature ranges of 340–420 °C under the strain rates of 10−2–101 s−1 by using a Gleeble‐3800 thermo‐simulator. The flow stress variation of high temperature and strain rate on the microstructure is analyzed. In the constitutive equation for the AZ80‐0.8wt%Y, it is conducive to obtain the deformation activation energy and the change law of strain of the material constant through the relationship between peak stress, deformation temperature, and strain rate. The deformation activation energy is found to be about 119.03 kJ mol−1. Subsequently, the values of the correlation coefficient (R) and the average absolute relative error (AARE) are 0.9826 and 7.29%, respectively. Consequently, the results indicate that the strain‐dependent constitutive equation has a good agreement with the calculated and measured flow stresses in the elevated temperature range for the AZ80–0.8wt%Y.