Abstract: Objectives Due to the broad application prospect of composite materials in ships, a composite sandwich structure filled with foam and ribs(combined thick plate) is designed.Methods Based on the anisotropic characteristics of combined thick plate, three-point bending and tensile tests on combined thick plate along the direction of the reinforcing ribs and perpendicular to the direction of the reinforcing ribs are conducted, the strength and modulus of the structure in different directions are compared. The failure modes and failure mechanisms of combined thick plate under bending loads in two directions are analyzed, and the effects of the center position of the specimen and the number of cell reinforced plates on their mechanical properties are discussed. Results The anisotropy of combined thick plate is significant. Compared to the longitudinal direction, the bending strength of the structure in the vertical direction of the reinforcement is increased by 82%, and the tensile modulus is increased by 22%. The results show that under bending load, the bearing capacity of the structure decreases significantly after the initial failure. The initial failure mode for the plate with perpendicular to the direction of the reinforcing bars is partial debonding of the lower panel, while the initial failure mode for the plate with along the direction of the reinforcing bars is failure of the reinforced panel due to shear.Conclusions The number of ribs in the cell and center position has a significant impact on the bending strength of the combined thick plate, but has a small impact on its tensile modulus. Under bending load, the initial failure mode of the structure is independent of the number of ribs in the cell and the position of the bending center. At the initial failure, there is no obvious buckling and fracture of the fiber, and the bending strength of the structure is determined to some extent by the adhesive strength between the panel, rib and foam. After initial failure, the damage process of the specimen varies. The results can provide technical reference for the promotion and application of composite sandwich reinforcement plates in the main load-bearing structures of ships and seas in the future.