Abstract: The spline finite member element method based on the potential energy principle for lateral buckling analysis of thin-walled members with arbitrary cross sections and arbitrary boundary conditions is proposed. A B₃ transformed spline function is used to simulate the warping displacements along the cross section of the thin-walled members, considering the effect of the shear strains of median surface of the members. It is able to describe the shear lag phenomena. To verify the proposed method, the stability of beams with irregular I-shaped cross section or L-shaped cross section is studied. It is shown that the present method is versatile, accurate and efficient.