[Objective] After the Wenchuan earthquake, a large number of debris flow prevention engineering were constructed. The numerical simulation of the effects of debris flow prevention engineering in strong earthquake areas was analyzed to provide a scientific reference for the study and prevention of debris flow.[Methods] Using FLO-2D software, this paper simulates the movement process and accumulation range of debris flow under different rainfall frequencies, and analyzes and evaluates the effects of debris flow in the prevention and control project, combining rainfall data, digital elevation model(DEM) and rheological parameters of debris flow, taking the "8·13" debris flow in Huangyang gully, Longchi Town, Dujiangyan City in 2010 as a typical example.[Results] Under the condition of prevention engineering, when the rainfall frequency P=5%, the discharge volume of debris flow decreased by 11.39 times and the accumulation range decreased by 6.14 times; when the rainfall frequency P=2%, the discharge volume of debris flow decreased by 4.18 times and the accumulation range was reduced by 2.7 times. The prevention engineering achieved certain control effects, but solid matter still rushed out of the ditch at the two rainfall frequencies.[Conclusion] Compared with the natural conditions, the volume and size of the rushing out of the debris flow significantly reduced. The prevention engineering is conducive to the prevention and control of the debris flow in the gully. However, there will have the possibility of solid matter rushing out of the ditch, due to the small capacity of the reservoir. Therefore, hazard mitigation measures such as monitoring and early warning systems need to be strengthened in the further governance of debris flows.