Abstract: An electrostatic precipitator is one of important environment protection facilities to eliminate the dust in atmosphere. The casing is the most important technical component. The casing wall being made of stiffened steel plates is connected with columns by continuous welding. The wall and columns form the structural system to bear loads cooperatingly. The transversal load of negative pressure and wind loading to which the casing is subjected are applied to the wall, and the vertical load is mainly applied to the columns. The initial imperfections on wall will influence the bearing capacity of columns. By the method of nonlinear finite elements, the influences of several imperfection forms on the bearing capacity of a column are investigated as the imperfection magnitude is varying, including the imperfection mode of limit point deformation of the perfect structure, the imperfection mode of nonlinear bifurcation point deformation of the perfect structure, the imperfection mode as eigenvalue buckling mode, the sine wave shape imperfection on wall, the residual deformation and residual stresses resulting from the welding shrinkage in erection process for wall. When the imperfection magnitude is determined, among all the geometrical imperfection forms, the imperfection mode of limit point deformation of the perfect structure is the most unfavorable. The bearing capacity of the column with the consideration of both residual stresses and residual deformation is slightly greater than the capacity with residual stresses being excluded. By increasing the magnitude of welding shrinkage, the residual stresses increase and the increment increases between the column bearing capacity with the consideration of both residual deformation and residual stresses and the corresponding capacity with the consideration of only residual deformation.