Abstract: Composite foam sandwich structures are widely used in aerospace due to their excellent performance, making it essential to quickly and accurately evaluate their bending characteristics. This study introduces a core stress state description term based on existing analytical theories and combines elastic and elastoplastic stress conditions of the core to derive theoretical formulas for composite panel wrinkling failure and elastoplastic foam core indentation failure. It improves the quasi-static bending analytical model of composite foam core sandwich structures by considering elastoplastic effects. Through high-precision finite element simulations and experimental verification, the following conclusions are obtained: For panel wrinkling failure, the elastic foam core is used to derive the deformation characteristics and failure load P_wk of the composite panel. The results are validated through finite element analysis, which shows that the panel wrinkling deformation is significant and the critical wrinkling load is in close agreement with the finite element calculations, and the prediction accuracy is superior to traditional analytical formulas. For the core indentation failure, the foam core is considered to exhibit elastoplastic behavior, and the structural yield load P_y at the transition point from elastic to plastic is derived. A prediction method for the core indentation failure load P_in is proposed, with the predicted critical load showing good agreement with experimental values. The method is further validated using multiple sets of experimental data for panels and core materials, demonstrating superior calculation accuracy compared to existing theoretical models and offering high engineering applicability.