During uniaxial compression tests of a twin-roll cast AZ31 alloy, the orientation induced anisotropy only lay in the initial strain range, which was attributed to the different twinning systems that were involved. Regardless of the initial orientation, contraction twinning always played an important role at higher strain range, especially with higher strain rate and lower temperature. At temperature higher than 300 °C, dynamic recrystallization would dominate. A single modified Arrhenius equation was used to describe the flow behavior for all experimental conditions. The n value was found to be higher at lower temperature when compression twinning was prevalent. Meanwhile the deformation activation energy was somewhat lower, which was attributed to the twinning induced softening effect.