Under the continuous influence of weathering and self-weight, there are a large number of cracks in the wall and roof of Beishan Cave 168 in Dazu Rock Carvings. These cracks lead to the deterioration of the stability of the surrounding rock at the top of the cave and the risk of instability and collapse. In order to effectively reinforce the broken surrounding rock of the roof of the flat-top grotto, this paper adopts a roof reinforcement method of suspended anchor in accordance with the geological conditions of the site. First, the main reasons for the cracking of the grotto roof are analyzed according to the distribution pattern of the roof cracks. Then, the anchorage length of the bolt is calculated by using the new Austrian method considering the most unfavorable surrounding rock stress. Finally, FLAC3D is used to analyze the displacement and stress changes of the grotto roof under rainfall conditions. The results show that the displacement of the roof in all directions is not more than 1 mm under the condition of suspended anchor reinforcement; the stress at the entrance of the grotto and near the inside of the grotto is relatively concentrated; the maximum tensile stress is less than the tensile strength of sandstone, and the roof surrounding rock is in a stable state; the average axial force of the bolt anchorage section is 31 kN. From the field monitoring data, it could be seen that the suspended anchor reinforcement reduces the fluctuation value of cracks. In summary, the grotto remains stable under the condition of suspended anchor reinforcement.