The samples having {0001} parallel to extruding direction(ED) present a typical true stress–true strain curve with concave-down shape under tension at low strain rate. Ultra-rapid tensile tests were conducted at room temperature on a textured AZ31 B magnesium alloy. The dynamic tensile behavior was investigated. The results show that at ultra-high strain rates of 1.93 · 102 s 1and 1.70 · 103 s 1, the alloy behaves with a linear stress–strain response in most strain range and exhibits a brittle fracture. In this case, {10-12} < 10-11> extension twinning is basic deformation mode. The brittleness is due to the macroscopic viscosity at ultra-high strain rate, for which the external critical shear stress rapidly gets high to result in a cleavage fracture before large amounts of dislocations are activated. Because {10-12} tension twinning, {10-11} compressive twinning,basal slip, prismatic slip and pyramidal slip have different critical shear stresses(CRSS), their contributions to the degree of deformation are very differential. In addition,Schmid factor plays an important role in the activity of various deformation modes and it is the key factor for the samples with different strain rates exhibit various mechanical behavior under dynamic tensile loading. The samples had {0001} parallel to extruding direction (ED) present a typical true stress-true strain curve with concave-down shape under tension at low strain rate. Ultra-rapid tensile tests were conducted at room temperature on a textured AZ31 B magnesium The results show that at ultra-high strain rates of 1.93 · 102 s 1 and 1.70 · 103 s 1, the alloy behaves with a linear stress-strain response in most strain range and exhibits a brittle fracture . In this case, {10-12} <10-11> extension twinning is basic deformation mode. The brittleness is due to the macroscopic viscosity at ultra-high strain rate, for which the external critical shear stress rapidly gets high to result in Because {10-12} tension twinning, {10-11} compressive twinning, basal slip, prismatic slip and pyramidal slip have different critical shear stresses (CRSS), their cont In addition, Schmid factor plays an important role in the activity of various deformation modes and it is the key factor for the samples with different strain rates exhibit exhibit various mechanical behavior under dynamic tensile loading.