Abstract: Carbon fiber reinforced polymer (CFRP) cloth reinforcement of precast concrete box girders is one of the commonly used reinforcement methods, however, the effects of the fiber laying angle and the number of fiber layers of CFRP cloth on the reinforcement effect have not yet been clarified, which restricts the optimal application of this reinforcement method. In this study, the effects of laying angle and number of fiber layers on the mechanical properties of reinforced concrete box girders were systematically investigated by numerical simulation. By simulating the reinforcement schemes with different fiber laying angles (orthogonal, diagonal and hybrid) and different fiber layers (2, 4, 6 and 8 layers), the mechanical property indexes such as initial stiffness, peak load and failure mode of the reinforced box girders were comparatively analyzed. The results show that the initial stiffness of the box girder after reinforcement with CFRP fabric is improved, but the increase is not more than 10%. The peak loads of specimens with orthogonal and hybrid fibers were increased by 40.19% and 38.26%, respectively, compared with the unreinforced specimens, and the peak load of the diagonal specimens was increased by only 16.27%, which indicated that the reinforcing effect was better when the fiber direction was parallel to the axial direction of the box beams (orthogonal). The damage of unreinforced or insufficiently reinforced box girders will only result in vertical cracks in the mid-span, whereas the damage of adequately reinforced box girders will also cause cracking in the web and flange of the box girder. The increase in the number of fiber layers has a significant effect on the specimen load carrying capacity enhancement, when the box girder is reinforced with 2, 4, 6, and 8 orthotropic layers of fibers, respectively, the peak load is increased by 14.69%, 40.19%, 42.15%, and 46.55%, respectively, compared to the unreinforced specimen. When the number of fiber layers exceeds 4, although the peak load of the reinforced box girder still increases with the increase of the CFRP fabric thickness, the increase is smaller, about 2% for every two additional layers. It can be seen that CFRP fabric reinforcement can significantly improve the mechanical properties of precast concrete box girders, especially the peak load, but there is a certain marginal effect. This study provides a theoretical basis for optimizing the design of CFRP fabric-reinforced precast concrete box girders, which helps to improve the reinforcement effect and economy.