Abstract: In response to composite tube with arbitrary lamination and thickness, an approach of the equivalent bending stiffness was presented. The deformation theory with realistic deformation of composite tube beam was used in this analysis. Transverse shear deformation, non-uniform torsion effects, the primary and the secondary warping effects and 3D elastic effects in laminate material were considered. According to the actual stress state of the shell wall, the caculation model of the equivalent bending stiffness of the composite tube was established. By comparison with three-point bending experimental data and the equivalent bending stiffness calculated by classical laminated plate theory of four composite tubes, the calculation model was validated. The application of the calculation model was analyzed by comparing degradation of the present theory with the calculation method of bending stiffness of isotropic material.