The invention provides a torsional beam. The torsional beam comprises a beam, and the beam comprises an inner side wall and an outer side wall, the section of the inner side wall presents as a wave shape, and the section of the outer side wall presents as a V shape. By conducting optimization design on the structure of the beam of the torsional beam, weight can be reduced, torsional rigidity can be improved and structural strength can be improved; therefore the relation of the weight, the strength and the torsional rigidity of the torsional beam can be effectively balanced.