Geological conditions of Jinping I Hydropower diversion tunnel is very complicated, it has the following characteristics, such as high geostress and developmental faults and joints, several collapse occurred in the construction process. A brief introduction is given to the geological conditions of Jinping I Hydropower diversion tunnel, based on discrete element method, Major joints and faults were simulated, and calculation models were built. By calculation and analysis, Rules and characteristics of deformation and failure for rock diversion tunnel has been obtained. After the diversion tunnel was excavated, high geostress were released, structural surface relaxation and slip. Side wall generated vertical cracks, vault take place chipping. With deformation increasing, the structural plane was further slip and open, dome support weakened, leading to collapse.