Weld-induced geometric distortion of plate between the stiffeners of fric tion stir welded (FSW) stiffened panel is idealized. The plate distortion magnitude is defined according to the statistical data from Paik′s analysis results. By the use of finite element method (FEM), the stability performance of FSW stiffened panel subjected to longitudinal compression is calculated and the effects of plate distortion shapes and boundary conditions on the stability performance of the structure are analyzed. Calculation results show that, in general, the plate geometric distortion presented in this work increases the critical buckling load but reduces the ultimate strength of the structure. The plate distortion shape affects the buckling mode and buckling load as well as the ultimate strength of the structure.