Abstract: Unstable rock mass is one of the main diseases threatening the safety of grottoes; therefore, revealing deformation and evolution characteristics of unstable rock mass is of great significance for rock stability evaluation and grotto protection. Taking a typical unstable rock mass in Yuanjue Cave of Anyue Grottoes, Sichuan Province as the research object, deformations of the upper, middle, and lower parts of the main control unloading fissure of the unstable rock mass were monitored precisely. Multi-source monitoring data was analyzed to explore deformation characteristics of unstable rock mass, combined with the systematic monitoring of environmental factors such as vibration, rainfall, temperature, and relative humidity. The results indicate that: Deformation damage of typical tension-shear toppling unstable rock mass was dominated by an unloading fissure. The opening width of the unloading fissure changes periodically with the seasons. In spring and summer, the opening width changes slightly in a wave-like manner, while during autumn and winter, the opening width decreases slowly in upper and middle parts and increases sharply in the lower part. A small overall opening width of the unloading fissure is observed, less than 1 mm, and the deformation amount and rate of unstable rock mass are much greater than those of the upper cliff. It also shows that deformation of unstable rock mass is sensitive to variations in external temperature and significantly negatively correlated with temperature. A sudden increase in rock deformation and restoration(0.06~0.2 mm) could be detected during rainfall. The deformation response of fissure width is obvious to rainfall, while weak to earthquakes. The unstable rock mass is still developing; oblique deformation occurs with the unloading fissure root as the axis, and it is likely to fall eventually. The results can provide a scientific basis for evaluating the long-term stable state of Yuanjue Cave and unstable rock mass research of grottoes.