Abstract: Taking Madaling landslide in Duyun Dity, Guizhou Province as an example, this paper simulated the excavation of coal bed based on Lagrangian fast difference algorithm of FLAC3D and revealed the deformation process and sliding mechanism of the slope. The results showed that (1) Coal bed excavation in Karst area has a significant impact on the stability of the slope. The excavation depth of coal bed controls the spatial distribution of vertical preferred structural plane of the slope body, the excavation width of coal bed controls the extension of vertical preferred structural plane, and the influence of the latter on the stability of the slope is much greater than that of the former;(2) The development process of Madaling landslide can be divided into two stages; (3)Due to unfavorable occurrence of stratum (NW282 ° < 18 °) and the existence of a large number of joint fissure water, a larger landslide disasters is being born.