Abstract: The deforming behavior of AZ31 magnesium alloy at different servo driving modes were studied by finite element method(FEM) and upsetting test, and the microsructure of the magnesium alloy before and after upsetting was observed. The results show that the damage of the sample deforming at the servo lower uniform speed driving mode and the servo decreasing-speed driving mode was decreased clearly at deformation temperature of 250 ℃, and the temperature difference during the deforming procedure and the deformation load were also decreased. The grain size of the sample at servo decreasing-speed driving mode was finer than that at the servo uniform speed driving mode, indicating that the servo decreasing-speed driving mode is in favor of the development of dynamic recrystallization of the magnesium alloy.