Variable cross-section member are widely used in engineering. However，the deformation calculation is complicated. In this paper，the Lagrange interpolation function was used to reflect the change of inertia moment and area in the element.The Hermite and Lagrange interpolation functions were then used to calculate the bending deformation and shear deformation. Consequently，the stiffness matrix of variable cross-section bending element，suitable for different variable cross-section member， could be obtained according to the principle of potential energy standing value. Finally，the stiffness matrix of variable cross-section bending element could be obtained considering shear deformation， while the balance condition of force and the geometric relationship of member deflection were analyzed. The self-made finite element program and the ANSYS were used to calculate the example，verifying the correctness of the element stiffness. It was found that the meachcanical performance of structure composed of variable cross-section is better than that of the structure composed of equal cross-section.