Abstract: The finite element method was used to analyze weak positions of load and deformation in the steel structure system of a large-scale selective catalytic reactor and study the buckling behavior of thin steel sheets with ribbed stiffeners. Based on these simulations, the stability of the sheets was discussed by experiment. The results indicate that the sheets are strengthened when rectangular holes are attached to ribbed stiffeners, which should choose L-ribbed stiffeners for the whole structure. The stronger the boundary constraint condition of thin steel sheets with ribbed stiffeners is, the bigger the critical buckling loading is, and the more difficult to buckle the sheets are. The experimental data are in better agreement with the simulation results.