Abstract: A mechanical analysis model for shear failure of CFRP sheets strengthened RC beams was established by using a three-dimensional (3D) meso-scale simulation method which considers the heterogeneity of concrete materials, the interaction between reinforcements and concrete and the interaction between CFRP sheets and concrete. On the basis of verifying the rationality of the meso-scale numerical method, the meso-models of 12 CFRP sheets reinforced RC beams were designed and established to explore the influence of different CFRP sheets reinforcement schemes on the shear performance and size effect of RC beams under monotonic load. In this investigation, all beams have the same CFRP fiber ratio (amount of CFRP sheets). The results indicate that: the CFRP strain distribution is closely related to the crack location, the closer the CFRP sheets to the crack location, the greater the CFRP strain; With the same CFRP fiber ratio, the reinforcement scheme with large width and small thickness of CFRP sheets is better than that with large thickness and small width; There is a size effect phenomenon in the shear strength of RC beams strengthened with U-shaped CFRP sheets. However, under the same CFRP fiber ratio, different reinforcement scheme has very little influence on the size effect of nominal shear strength and thus can be ignored.