Abstract: To investigate the influence of underground mining activities on the deformation of overlying strata and mountains in karst mountainous areas, the “8.28” landslide in the Pusa community in Nayong County of Guizhou is taken as an examplein this paper, and on the basis of field geological survey, the characteristics of the collapse body and the deformation development process of the mountainsare expounded. The UDEC discrete element numerical simulation is used to simulate and analyze the process and mechanism of landslide instability induced by mining in underground mines. The results show that this mountain karst erosion is strong, there are many ground fissures and karst collapse pits, and rock mass is broken. Before the collapse, the rock mass has experienced a long deformation development process, which was obviously affected by underground mining operation. The overlying strata of the mountain deform towards the direction of goaf under the underground mining operation. With the roof rock falling, the rock deformation increases significantly. Deep and large karst mountain fissures in the overlying strata have important effects on mountain deformation. After mining, the upper rock layer forms a subsidence zone along the fissures and the fissures expand. As a result of excavation unloading, the leading edge rock mass in the collapse zone extruds out of the slope, and the resistance sliding force of the leading rock mass decreases.With the continuous expansion of the goaf, the stability of the mountain continues to decline, the final overall collapse and destruction occur. The landslide mode of Pusais thought to be “pull crack subsidence at the back edge of mountain-fissure spreading through-overall collapse”. This study is of great significance for the evaluation of the influence of underground mining on the stability of karst slopes in southwestern China.