Abstract: The variation law of strength and plasticity of a low alloy steel in tensile test following torsion was studied.The hardening effect of torsion techniques and the exertion of plasticity were analyzed quantitatively and the reasonable combination of strength and plasticity has been discussed.When material is hardened by torsional prestrain in engineering,the multitude of prestrain should be as high as possible and at the same time microcracks on the surface of specimen should be avoided,in order to get an optimal combination of strength and plasticity.A torsional prestrain of 8π was optimal to the tested steel in terms of reasonable combination of strength and plasticity.