Abstract: The ultimate performance of H-sectional steel beam-columns bent about the strong-axis was thoroughly investigated. Based on a verified finite element model, parametric analysis of H-sectional members with different combinations of flange and web width-to-thickness ratios as well as different axial force rations was conducted, and the failure mechanism was derived from the stress development curves. It was found that in the ultimate stage, the stress distribution was significantly affected by the local buckling mode, which turned out to depend on the flange-web interaction. Thus, it is necessary to take the flange-web interactive effect into consideration when calculating the ultimate strength. Finally, based on the stress distribution property in the ultimate state, a calculation approach to calculating the ultimate moment denoted as “effective-plastic-width method” was proposed. This approach was validated through comparison with experimental results and FEM analysis.