Deformation twinning of homogenizing magnesium alloy AZ31 is respectively investigated by compression at room temperature with different deformation degrees from 5% to 15% and different deformation rates from 0.5 to 4mm/min.The results show that thick twins exit in a few amount of crystals at the beginning of the deformation.The thin-long twins and the thick twins appear at the end of the deformation,and they can be observed in almost all crystals.With increasing compressing rates,the yield strength,compression resistance fracture strength and density of twins increased,and twins become thin.