The ultimate strength of a stiffened panel with beam-column buckling is investigated using the beam-column approaches. The ultimate strength of the beam-column is obtained by the analytical formulas (the Johnson-Ostenfeld Formula and the Perry- Robertson Formula) and finite element method, which incorporates the effective width formulas (Von Karman and the Winter formulas) here. Meanwhile, a novel numerical method is developed to calculate the effective width of the beam-column. Furthermore, the ultimate strength of the whole stiffened panel is deduced using that of the single beam-column. Comparisons between these proposed methods and the nonlinear finite element analysis (the CAE software is ABAQUS) are performed. The results show that good accuracy can be achieved using the proposed methods, especially for the beamcolumn approach based on the finite element analysis. It suggests that the methods can predict the ultimate strength of a whole stiffened panel accurately and effectively.