Abstract: The dynamic recrystallization behavior of short carbon fiber(CF_s)/AZ91D composite and AZ91D Mg alloy was investigated by isothermal compressive experiment at the deformation temperatures from 340℃ to 400℃, strain rates from 0.001 s^-1 to 1 s^-1 and a maximum true strain of 0.7. The results show that both CF_s/AZ91D composites and Mg alloy exhibit an obvious dynamic recrystallization during being compressed at elevated temperature. The addition of CF_s greatly promotes the dynamic recrystallization of the matrix alloy in the composite. As a result, the critical strain for dynamic recrystallization is reduced and a finer recrystallized grain structure is obtained in the composite. For the Mg alloy, the variation of volume fraction of dynamic recrystallization with the strain presents the classical "S" mode. For the CF_s/AZ91D composites, however, the increase of volume fraction of dynamic recrystallization with the increase of strain exhibits a rapid-slow-stable behavior. The dynamic recrystallization critical strain and kinetics models of CF_s/AZ91D composite and Mg alloy were developed according to the experimental results. Based on these models, the difference of the dynamic recrystallization behavior between CF_s/AZ91D composite and Mg alloy was analyzed.