This paper studies the buckling of stiffened lower panel of center wing box with multibeam under compressive loading. For the effect of end support, lateral support and curvature for the buckling of panel, the end support fact of critical compressive stress formula of stiffened panel in current design manual was analyzed, and proper buckling stress of stiffened panel was obtained. The result shows that the end support , lateral support and curvature of skin make a significant effect on the stabilization of stiffened panel under compressive loading, and for the stiffened panel with thick shin, the end support fact is advised to be 1.5～2.0.