To explore the load-bearing performance and the role of plate components in H-shaped section bending members, four-point pure bending tests were conducted on four welded H-shaped steel beams with different flange and web width-to-thickness ratios. The failure mode, force-displacement curve, ultimate bending capacity, and ductility of the test pieces were analyzed. By comparing the strain development and single plate bearing capacity of the web plates under different flange support conditions with the same dimensions, the mechanism of plate component interaction in this situation was revealed. Based on the experimental results, a calibrated finite element model was established using ABAQUS, and parameter analysis was conducted using this modeling method. By separating the flange and web plate bending load capacities of the parameterized components, the law of plate component interaction under bending conditions was further explored. The experimental and parametric analysis results both indicate that the occurrence of local buckling in the plate elements generally corresponds to the ultimate bending capacity of the H-shaped section members. The width-to-thickness ratio of the plates is a significant factor affecting local buckling. Furthermore, the interaction between the plates manifests as plates with different width-to-thickness ratios influencing the buckling timing of adjacent plates by altering the constraints on them, which affects the load-bearing capacity of individual plates and thus impacts the overall load-bearing performance of the member. Finally, based on the parameter analysis results, the ultimate load-bearing capacity of the members was normalized, and an S2-S4 grade section classification method considering the interaction of plate elements under bending conditions for H-shaped sections was proposed. The comparison results show that the section classification limits proposed in this paper match well with the experimental results and can reasonably reflect the impact of plate element interactions on the actual load-bearing capacity of the section.