After the Wenchuan earthquake， a great volume of loose material caused by co-seismic land⁃slides mantle on the slopes or in the channels，which in later years served as debris source for rainfall-in⁃duced debris flows. Flood and debris flows would erode the mobile bed violently that is composed by these loose masses，enlarging debris flow scale and making the flow resistance characteristic different from that on the fixed bed. The characteristics of flow resistance and magnitude were examined by analyzing debris-flow events happened after the earthquake. It is found that Darcy-Weisbach resistance coefficient shows a close relationship with sediment discharge and Froude number by regression analysis of the data of 6 events. Moreover，regression analysis of 16 events in Qingping and Beichuan shows that there existed a good power exponent relationship between magnitude，rainfall and catchment area. The research results are useful for debris flow disaster prevention and mitigation.