The aim of this study was to analyze the ultimate strength of stiffened aluminum panels by the non-linear finite element method. A new type of stiffened aluminum alloy panel has been designed which has fixed longitudinal and alternating floating transverse frames. Based on material tensile tests, the material properties of the aluminum alloy were obtained. Then, the simulation method of welding residual stresses and the effect of heat-affected zone are investigated. The FEA software ABAQUS V6.11 is used to estimate the ultimate strength of these stiffened panels under axial compression. The results show that: 1) The mechanical imperfections have significant effect on ultimate strength of stiffened panels; 2) residual stresses may have positive effect on ultimate strength; 3) the new stiffened panels also have good performance on ultimate bearing capacities.