Abstract: A cross-section of the column in the enclosure structure of electrostatic precipitator casing is composed of double H-shaped limbs as it needs to support the top beam with a wide box section and bear large axial compression. The nonlinear finite element method was used to investigate the stability of the composite section column subjected to axial compression in consideration of the initial imperfections. The research results showed that the residual stresses caused by column rolling and the welding between wallboard and column had a slight adverse influence on the buckling capacity of the column. The column presented the interactive buckling in the top span, that is, the overall flexural-torsional buckling occurred on the T-shaped section composed of the front flange, and the front half web and the local buckling occurred simultaneously on the web. Wallboard and the connecting wallboard as stressed skin plates, shared part of the load and restrained the lateral deformation of the column. The stability of the column increased when the connecting wallboard was close to its front flange. Factors such as the connecting wallboard width, the wallboard width, the stiffness of the angle stiffener and the thickness of the joint plate slightly influenced the stability of the column. When the thickness of neighboring wallboard and neighboring connecting wallboard increased, the stability of the column increased. However, the thickness of the wallboard far from the column had little influence. The buckling factor of the column did not change monotonously with the increase of the width to thickness ratio of the flange. However, it decreased with the increase in the flexural slenderness ratio of the H-shaped limb round its weak axis and the height to thickness ratio of the web. Based on a large number of the nonlinear finite element computation results, an evaluation method was proposed for the buckling bearing capacity of the column composed of double limbs in precipitator casing under axial compression.