Abstract: Many causative factors have changed acutely after the Wenchuan earthquake. They included the loose material, micro-topography and hydrological environment. Hence, the earthquake-induced debris flows are different from the general one. A whole debris flow process mechanism is developed and analyzed quantitatively using initiation discrimination model, bed-matrix erosion model and outburst-discharge enlargement model. It includes the initiation, transition and deposition phases. Moreover, the failure mechanism of the erosion-outburst-induced debris flow is illustrated clearly with an example. The result indicates that bed-matrix entrainment mechanism is the comprehensive outcome of the stress enlargement, strength degradation and material basis. The landslide dam outburst-induced discharge enlargement and the above-mentioned erosion mechanism are contributed to the large-scale debris flow. The case study of Hongchun catchment indicates that debris-flow discharge increases to 800.80m³·s^-1 due to H02-03 landslide-dam outburst, and the entrainment-induced solid materials are half of the total magnitude, about 34.72×10⁴m³.