Abstract: After Wenchuan earthquake,a large number of various types of debris flow occurred in Wenchuan earthquake region.Firstly,the paper analyzed the characteristics of urgent steep gully debris flow,such as small catchment area,large longitudinal gradient,abundant loose materials,strong erosion and the large run-out scale.Then taking Wayao gully as a typical example,the basic characteristics and formation conditions were identified.Using FLO-2D software,a simulation of the dynamical process of urgent-steep channels featured debris flow during 50-year rainstorm conditions was set up.The paper analysed dynamic characteristics,initiation,erosion and deposition of debris flow in Wayao gully.The results show that the depositions of downstream are generally 3—5 meters high and the maximum velocity is 9.34 m/s.The amplitude of scour and accumulation is large and the hydrodynamic force is strong.Therefore it is important to assess debris flow risk and take hazard monitoring and early warning for debris flows with urgent channels in the earthquake areas.The effective combination of control work is also necessary for debris flow hazard mitigation.