Abstract: In order to reveal the shear mechanism of the carbon fiber reinforced polymer (CFRP) grid-polymer cement mortar (PCM) shear reinforced reinforced concrete (RC) beam and establish its bearing capacity calculation method, four-point bending tests and finite element simulation were conducted on the RC beams. The shear contribution of the CFRP grid to the RC reinforced RC beam was analyzed, and the shear bearing capacity calculation method was established based on the improved truss arch model. The results show that the CFRP grid-PCM reinforcement layer can not only inhibit the development of inclined cracks, but also improve the shear bearing capacity. CFRP grid and reinforcement have good cooperative working performance, where the horizontal CFRP grid shares about 16% of the stirrup strain. Regression analysis indicates that the strain of the vertical CFRP grid is about 0.29 times than that of the horizontal CFRP grid. Comprehensively considering the dowel action of the longitudinal CFRP grid and the stirrup strain shared by the horizontal CFRP grid, the bearing capacity calculation method is presented based on the improved truss-arch model, which has better applicability and accuracy to meet the design requirements.