Abstract: Numerical simulation is an important tool in the investigation of high-speed long-runout landslides. Taking the Xinmocun landslide in Maoxian as an example, this paper proposes a 3-dimensional discrete element modeling and numerical simulation method of large-scale landslide. On the basis of the micro-macro conversion formulas and numerical tests of discrete element method, it is able to get a discrete element deposition model that has similar mechanical properties as the sandstone of the landslide. Combined with the digital elevation model data and strata information, a 3-dimensional discrete element shell model is built, which follows the actual strata condition and rock mechanical properties. The initiation, high-speed sliding and accumulation process of Xinmocun landslide is simulated. The simulation results and the actual landslide accumulation are very similar in pattern and distribution, and the characteristics of velocity variation and time scale of simulated landslide coincide with the theoretical values and the measured seismic signal, which validate the reliability of the numerical simulation results and the effectiveness of the method. Source code of the numerical simulation is shared online(http://matdem.com), with which a three-dimensional model can be built quickly. This paper provides an alternative approach for the study of mechanism of high-speed long-runout landslide and the evaluation of corresponding disaster effects.