Abstract: [Objectives]This study aims to research the influence of lateral loads on the ultimate strengths and failure mechanism of stiffened panels subjected to combined loads. [Methods] Nonlinear finite element software ABAQUS is used to set up numerical models and perform numerical simulations under combined loads on different models. The out-of-plane displacement fields are captured, and decomposed with buckling modes. [Results] The modal amplitude-axial load curves of different models are obtained, and the deformation process of stiffened panels is quantified. The deformation behaviors and collapse modes of stiffened panels in different load cases are analyzed combining with cloud diagrams. [Conclusions] The lateral loads in combined load cases cause the yielding of the stiffeners at the endings before the ultimate state, resulting in the increase of the overall buckling mode’s amplitude. As the lateral load increases, the overall buckling of the stiffened panels become the dominant collapse mode under combined load cases.