Abstract: Many kinds of complex rockfall geological disasters are induced by the mining at the upstream side of the Yangshui river basin in Guizhou province. The cracking-topple model of failure is taken as an example in this article. Based on the analysis of slope structure, the process of the rockfall developing is studied. It includes the exerted force, the compression and the dilatancy in rock mass. During the study, the spacing-stress-analysis theory of rock mechanics is used. The DEM simulation is used to verifying the deformation behavior and failure mode. The conclusion can be drawn as follow. The rockfall is triggered by the Phosphate mining. Then the stress-strain adjustment and deformation of the rock mass are caused so that the rock mass dilatancy leads to instability of rock dumping, and then cause collapse. The process of load and deformation can be divided into four phases as follows. The discontinuities are stretched and cut through. The compressed rock mass deformed. The rock mass gets dilatancy. And the rock mass gets failure. The adjustments of the stress and strain, the deformation and the cracks influence each other.