Abstract: In order to study the bending failure mechanism of composite sandwich panels, the fiberglass- polyurethane foam sandwich panel is designed and manufactured by vacuum infusion. A theoretical model for its failure is built and the bending test is carried out, as well as the numerical simulation. The failure load is obtained, and two failure modes are revealed during the bending process. An explanation of two inflexion points observed in the load-deflection curve of the glass fiber-polyurethane foam sandwich panel is made. It is concluded that the first inflexion point, corresponding to the first failure mode, is owing to the tensile splitting of the surface glass fiber, and the second one, corresponding to the second failure mode, is due to the shear force splitting of the middle foam.