Abstract: To study the torsional properties of RC beams strengthened with carbon fiber reinforced polymer (CFRP) sheets under flexural, shear and torsional conditions, a meso-scale numerical analysis model was established to reflect the heterogeneity of concrete materials, the bond slip relationship between steel bars and concrete and the interaction relationship between CFRP sheets and concrete. Due to the lack of typical physical tests of RC beams strengthened by CFRP sheets under flexural, shear and torsional composite forces, the rationality of the numerical model was verified by composite comparison verification method. That is, the results were compared with the experimental results of RC beams and CFRP sheets strengthened RC beams under single shear, single torsion and flexural-torsion composite loadings. Then, based on the established meso-scale numerical analysis model, effects of fiber ratio and torsion-bending ratio on the torsional mechanical properties of RC beams strengthened by CFRP sheets under combined bending, shear and torsion were investigated. Results show that: 1) the peak torque of RC beams can be significantly improved by using CFRP sheets; 2) with the increase of fiber ratio, the damage distribution range of RC beams gradually becomes larger, the CFRP strain gradually decreases, and the overall peak torque of the beam increases, but its increase amplitude decreases; 3) with the increase of the torsion-bending ratio, the crack distribution of RC beams becomes more concentrated, the angle between the crack and the horizontal direction gradually decreases, the peak torque of the beam increases, and the CFRP strain monotonically decreases. The numerical simulation method considering flexural, shear and torsional composite forces established in this paper can lay a foundation for the subsequent research on the size effect behavior of RC beams strengthened by CFRP sheets under complex stress states.