The Wenchuan earthquake triggered many landslides in the Longmen Mountain area. Among them, landslide #1, which had a unique failure model, occurred in the Liujiawan area, Qingchuan County, and experienced two failure processes. First, the shallow surface phyllitic slate and slate generated coseismic landslides, and then, the outcropping dolomite generated another landslide accumulation process at the slope foot. Landslide deposits formed a two-stage accumulation platform with different lithologies, and this structure was extremely rare among large coseismic landslides triggered by the Wenchuan earthquake. The numerical simulation results verified the unique failure process of landslide #1. The study results are helpful in further understanding landslide disasters caused by strong earthquakes and the disaster formation process.