On 12 May 2008, the extremely strongWenchuan earthquake triggered thousands of landslides, and produced large amounts of loose soil material that remained deposited on the steep slopes and in the gullies.As a consequence of the heavy rainstorms during the rainy season, numerous debris flows occurred in the earth-quake zone. Previous studies have shown that the significant feature of these debris flows was that they were further transformed from existing landslides triggered by theWenchuan earthquake.To analyze the dynamic behavior of the debris flow during the propagation, a numerical model based on Smoothed Particle Hydrodynamics (SPH) is presented to simulate massive debris flows across 3D terrain. The Navier-Stokes equations and the Bingham model are used as governing equations and constitutive equation respectively. The SPH model is applied to simulate typical post-earthquake debris flows in earthquake-hit are-as called Wenjia Gully debris flow. The whole flow processes of the loose soil material combine with the rainwater across the 3D terrain are represented. The shape of the deposition zone was investigated. Comparison of the SPH simulated geometry and the surveyed data was conducted, and showing a high degree of similarity. This indicates that the SPH model can accurately represent the evolution of the final deposition shape. The prediction of the propagation of post-earthquake debris flows can notably reduce sudden loss of life, as it provides a means for mapping hazardous areas, for estimating the hazard intensity, and for identification and design of appropriate protective measures.