Abstract: The Niwangou ditch is the first tributary of Bailong River, where the geological structures are very developed and the loose materials are abundant. In history, there happened several large-scale debris flow disasters, which belong to typical rainstorm viscous debris flow. For the better benefit evaluation of debris flow control engineering, the FLO-2D model has been applied to simulate and compare the debris flow movement, accumulation, and risk under different frequency before and after the treatment. The results show that the loose material originally accumulated at the exit of gully will be intercepted in the dam body with the volume of 3.97×10⁴ m³ by the control engineering. Moreover, the flow velocity of debris flow can be effectively controlled, and the maximum flow velocity at the exit of gully is 2.7m/s when the rainfall frequency is 1%. And this engineering will limit the accumulation range of debris flow, the reduction ratio can be greater than 84%. The method is not only to the benefit of evaluation of debris flow control engineering, it also provides the effective data support to the treatment scheme. Overall, the evaluation method is a worth reference by researchers.