Abstract: The stress analysis of carbon fiber sheet(CFS) strengthened reinforced concrete(RC) box girders subjected to combined loadings is conducted.Based on the diagonal-compression-field theory considering concrete softening,the stress analysis method of CFS strengthened RC box girders under the combined loadings of the bending moment,shear force and torque is established,the corresponding computer program was developed,and the numerical investigations of four experimental models of CFS strengthened RC box girders subjected combined loadings were carried out.The comparisons of the calculated and the experimental results shows good agreement,the average ratios of the experimental and calculated results of the torsion angle within unit length of the specimens range from 0.846 to 1.064,and its mean square deviations range from 0.071 to 0.177;the average ratios of the experimental and calculated results of the strains in the longitudinal bars range from 0.946 to 0.997,and its mean square deviations range from 0.051 to 0.093.The established stress analysis method is reasonable and feasible for CFS strengthened RC box girders subjected to combined loadings.