The rock structures at Pusa Village, located in the karst mountainous area of Nayong County, Guizhou Province, China are gently dipping. The upper part of this mountain is composed of hard rock layers while the lower section is made up of soft rocks which includes six (6) coal seams. Mining the coal seams excited the rest of the slope body leading to instability of the upper portions. On August 28, 2017, a massive landslide occurred in this area which resulted in the generation of 82, 500 cubic meters of debris. Significant casualties and social impacts were recorded. Twenty-six (26) fatalities and nine (9) missing people were reported. In this paper, the field engineering, geological conditions and long-term mining activity are investigated. A numerical model is developed to simulate and analyze the failure and deformation process of the Pusa collapse. The failure factors of the Pusa collapse can mainly be attributed to the unique geology of the slope rock mass, underground mining activities, topography and rainfall. The intensified mining activities increased the compressive stress in the upper layers and caused the development of fractures and cracks. The failure process of the Pusa collapse can be summarized into three stages, namely: (1) deformation of the roof layers, (2) cracking on the crest of the slope, (3) rapid deformation and collapse. The upper slope with high strength rocks developed crack—toppling failure while the lower slope with low strength rocks developed crack-slide failure. In summary, the slope deformation and failure mechanism are tensional, toppling, and shear failure.