Abstract: The classification of cross-sections is an important basis for contemporary design specifications of steel structures. The relevant provisions of the current steel structure specifications on the cross-section classification of H-section steel beam-columns were reviewed. It was found that most of the specifications follow the individual plate rule. Based on a verified finite element model, a parametric analysis of H-section members with different combinations of flange and web width-to-thickness ratios as well as different axial force ratios was conducted. Through the simulation results it was observed that different width-to-thickness ratios and axial force ratios could lead to different failure modes and strength. This confirmed the interaction effect of adjacent plates on the classification of cross sections. A classification method for S2, S3, S4 and S5 sections under combined axial force and bending moment around the strong axis of H-section steel members based on the ultimate strength was proposed. Compared with various specifications and experimental results, it is shown that the proposed cross-section classification method represents the response conditions of the plates, which confirms the necessity of considering the interaction effect of adjacent plates.