Subjected to various natural forces, the disease of grotto temple is serious. The damage degree of grotto temple is increasing with time, and the preventive protection for grotto temple is becoming more essential. The preventive protection measures mainly consists of the numerical evaluation and on-site monitoring. In order to ensure the accuracy of numerical calculation, this paper proposes the following methodology: First, the three-dimensional laser scanning cloud image of the grottoes temple is used to generate a fine geometric model of the grottoes temple to accurately reflect its complex geometric shape; Secondly, H-B criterion is used to fully consider the deterioration of rock mass mechanical properties caused by weathering, cracks, joints and other diseases, and to obtain reliable rock physical and mechanical parameter, and then establish a refined numerical calculation model that more truly reflects the boundary conditions, stress displacement and possible failure path. Finally, the current stability of the grotto temple is analyzed by strength reduction method, and the danger zone of the grotto after the deterioration of the rock mass is predicted by the longitudinal wave velocity of the rock mass, and an early warning system is established to realize the preventive protection of the grotto temple. Taking Grottoes No. 9 and 10 of Yungang Grottoes as an example, systematic modeling, force analysis and stability discussion are carried out by using the above research ideas. The results show that the grottoes maintain a stable state as a whole at present, and stress concentration exists in some areas. By simulating rock strength deterioration, the potential instability risk area of the cave is predicted, and an early warning system based on rock P-wave velocity is established.