Abstract: Compared to general high slopes,there is an obvious difference in the material composition,boundary condition and mechanical character for deposit slopes.Because of the obvious discontinuity character of deposit slopes in terms of deformation and failure,it is difficult to reveal its failure mode and process for conventional stability analysis method.The discrete element method(DEM)can provide an optimum solution to problems such as deformation and failure of discontinuity.Firstly,based on a large-scale complex slope in debris deposit,a numerical test is carried to simulate triaxial test of deposit soil.Micromechanics parameters are determined through comparison to the laboratory test results.A general study on its failure mechanics was carried out using DEM.Failure mode and deformation process were also involved.The results show: the slope before excavation is stability.There are two potential slides mass on the upside of slope after first step of excavation showing deep sliding along bedrock underlying debris deposit.There is an obvious slide mass at the bottom of slope after second step of excavation.Its failure will speed deformation and sliding of two potential slides.For the whole slope in debris deposit,its failure mechanics mainly shows in a gradual deformation and failure mode along contact surface from bottom to upside.