Abstract: This paper proposes an approach to analyze the mechanical characteristics of the thin-walled I-beams with wide flange. Two different longitudinal displacement difference functions ( , ) are considered to account for the change of shear lag in the thin-walled I-beams with various widths of wing slabs ( ). The energy variation principle is applied to establish the governing differential equations and corresponding natural boundary conditions on the static and dynamic characteristics of thin-walled I-beam, and closed-form solutions of generalized displacements are obtained. The finite shell element solutions are compared with the analytical solutions of this paper and the proposed approach is validated.