Abstract: The Beishan Cave 168 of Dazu Rock Carvings is a five-hundred Arhat Grotto, excavated between 1119 and 1125. The cave is 3.3m high, 3.14m wide and 7.1m deep. It is an important cave with a larger size among the Dazu Rock Carvings. At present, the weathering disease and fissures in the surrounding rock mass of Cave 168 are very serious, and are in danger of collapse. In order to formulate targeted long-term protection measures, it is necessary to find out the current situation of the disease in the surrounding rock mass of Cave 168. Through on-site investigation, geophysical prospecting, drilling and other technical means, the engineering geological conditions of Beishan Cave 168 and its adjacent areas have been obtained. Furthermore, in order to reveal the weathering status of the rock mass on the top of the cave and the development of joint fissures in the rock mass, Rayleigh wave phase velocity imaging on the roof rock mass of Cave 168 is performed with high-frequency Rayleigh wave detection technology. In consideration of the specific surrounding rock boundary conditions and site engineering geological conditions of the rock mass on the roof of Cave 168, the origin analysis and interpretation of the distribution of the low-velocity zone in the Rayleigh wave phase velocity-depth imaging profile of the cave roof rock mass were developed. The results out of the work mentioned above may provide basic geological data and necessary calculation parameters for the analysis and evaluation of cave surrounding rock mass stability and stone carve protection engineering design, and also provide experience and reference for the application of related technologies in cultural relics protection projects.