In the mountainous area of southwestern Sichuan, influenced by tectonic erosion and denudation, the terrain on both sides of the rivers is strongly cut, with high mountains, steep slopes, and crisscrossing valleys. Debris flow gullies are well-developed, showing diverse types. Although one type of debris flow has a small drainage area and short gully channels, due to its steep slope gradient, it possesses high potential energy once occurred. The impact range of this type of debris flow is highly uncertain, posing significant challenges to prevention and control efforts. It also has a considerable impact on people's lives and property, as well as engineering construction. Taking the debris flow in Gaye Gully, Keljin Village, Geshzha Town, Danba County as an example, through investigation and analysis of its main development characteristics, numerical simulation technology is used to evaluate its danger based on on-site and indoor test results. The danger level is defined based on the accumulation depth of the debris flow and the product of the accumulation depth and flow velocity. The study has reference significance for analysing the risk evaluation of similar debris flow characteristics.