Landslide disasters, one of the most destructive geo-hazards, often have serious consequences that range from economic losses to fatalities. Earthquakes, particularly those with strong ground motion, can trigger thousands of landslides in mountainous regions. The 2008 Wenchuan earthquake which occurred in China is such an example. The massive Daguangbao landslide is the largest landslide that occurred in this earthquake and it is modeled in this paper suing a 3D using the Material Point Method (MPM). Focus is on the failure mechanism and the run-out process of the failed mass due the earthquake interaction on the slope. The 3D model was developed considering the spatial variation of the materials into the domain. The constitutive modeling of the materials includes elastoplastic constitutive models with linear-softening and rock tensile strength cutoff. The numerical results in 3D are compared with previous results in 2D and with the reported topography of the characteristic section of the slope. The numerical results allowed estimating the onset and evolution of the failure surface and the formation of fragmented blocks. within the failing mass. This work also addresses a discussion about results and conclusion.