Aluminum has become the material of choice for many types of vessels, particularly high-speed vessels where lightweight structure is important for meeting design goals. The methods of design and fabrication of aluminum contain many areas of conservatism that if overcome by proper research will lead to even greater performance at reduced cost. This paper studies the ultimate strength of Aluminum stiffened panel under combined loading conditions. A Finite Element Model had been developed based on published experimental study, this model was validated by comparing the output results with experimental work. The model calculated the ultimate strength of the panel under axial load. After validation of the model, it is used to estimate the ultimate strength of the aluminum stiffened panel under combined load. It is intended to investigate the effect of initial imperfection on the ultimate strength of the aluminum panels into the finite-element models studied. The effect of change in panel aspect ratio and the effect of column slenderness ratio are investigated. It has been found that an increase in aspect ratio affects the ability of the panel withstand any increase in load especially in case of imperfections. The analysis for the force-displacement relationships and post-collapse deformed shapes is also investigated.