Abstract: The failure modes of sandwich beams with Balsa core are analyzed. The sandwich beams fail in several modes including the core shearing, the tensile/compressive failure of face sheet and the face sheet bulking. The tests demonstrate that the capacity of sandwich beams with Balsa core is greatly lower than that predicted theoretically and the failure modes are different from those of the common sandwich beams. The finite element analysis is performed considering the imperfection of the composite structure. Several FE models including the anisotropy and the initial imperfection are built up. The curve fittings of the numerical results are performed by means of the neutral network technique. The influence of the initial interfacial delaminations and the core cracks are investigated.