Abstract: Fly ash cenosphere(FAC)/AZ91D Mg alloy composites were prepared using stir casting method. The high-temperature compression deformation behavior of FAC/AZ91D Mg alloy composites was studied, the influences of compression deformation temperature and strain rate on compression deformation behavior of FAC/AZ91D Mg alloy composites were analyzed, and the thermal deformation activation energy was calculated. The results show that the high-temperature compression true stress-true strain curves of FAC/AZ91D Mg alloy composites can be divided into four stages: elastic deformation, work hardening, peak stress and steady-state flow stage. At the same strain rate, the peak stress and steady-state flow stress of FAC/AZ91D Mg alloy composites decrease with increasing compression deformation temperature; at same compression deformation temperature, the flow stress increases with increasing strain rate. At the same strain rate or the same compression deformation temperature, the hot deformation activation energy of FAC/AZ91D Mg alloy composites increases with the increase of the compression strain rate or the compression deformation temperature. The thermal compression behavior can be described with Arrhenius relationship with hyperbolic sine function form. Both compression deformation temperature and the strain rate have important effects on the high-temperature compression structure of FAC/AZ91D Mg alloy composites. Increasing the compression deformation temperature or the strain rate can accelerate the process of dynamic recrystallization.