Hot compression tests of AZ91D magnesium alloy were performed on Gleeble1500 ranging from 0.001 to 1 s-1 and deformation temperature ranging from 200 to 400°C. The results show that flow stress is dependent on deformation temperature and strain rates．When strain rate is a constant, flow stress decreases with the increasing deformation temperature. Meanwhile, as deformation temperature is a constant, flow stress increases with the increase of strain rate, which can be demonstrated by a Zener-hollomon parameter in the hyperbolic-sine-type equation during hot compression deformation. The hot deformation activation energy is 176.01kJ/mol and the stress exponent is 7.85 during hot compression deformation of AZ91D magnesium alloy.