Abstract: Debris flow is one of the frequent geological disasters in southwest mountainous areas of China. It is characterized by sudden occurrence, fast velocity and strong destructive force, which often causes huge casualties and economic losses. Risk assessment of geological hazards is one of the effective measures in disaster prevention and mitigation management and prevention, which can reasonably quantify the spatial distribution characteristics of debris flow hazard along the debris flow movement and accumulation route. Taking Maliu gully in Longchi Town, Dujiangyan City, Sichuan Province as the research object, slope, plane curvature and upslope catchment area were selected as the identification factors for the initiation area of gully debris flow. Based on the starting point of debris flow identified by Flow-R model, the FLO-2D model was coupled to simulate the movement and accumulation process of debris flow in Maliu gully. The debris flow hazard can be determined by combination of accumulation depth, velocity and outbreak frequency of debris flow. In addition, the accuracy of the simulation results was assessed by confusion matrix.The results showed that the simulation results of Maliu gully debris flow by Flow-R and FLO-2D coupling models was in good agreement with the actual conditions. The simulated debris flow accumulation area is 2.19×104m2, and the accumulation volume is 4.92×104m3. The debris flow risk gradually decreases from the center of the channel to both sides. High risk area accounts for 42.3%, medium risk area accounts for 23.1%, and low risk area accounts for 34.6%. In formation area and circulation area of Maliu gully, the volume of scattered accumulation materials in the channel is about 300000 m3. The Maliu gully debris flow is still in a highly active stage with high risk. In the future, under the condition of sufficient rainfall and hydrodynamic force, a large quantity of loose materials may be reactivated, which may cause major geological disasters once it occurs.