A method of redesigning the front rail using tailor-welded blanks was studied, in order to reduce the weight of front rail and enhance its crashworthiness on conditions of satisfying strength and stiffness requirements. By CAE analysis of stress distribution in the rail in the case of self-weight, the number of parent sheets and weld line distribution were determined. By establishing the constraint inequalities of strength, bending stiffness and torsion stiffness, the thickness determination was performed. The full-width frontal impact simulation of the whole car after redesign in the front side rails shows that the front rail of tailor-welded blanks has a better crashworthiness in comparison of original design, while it has a lightweight effect of 17.7%.