Abstract: The Bailong river basin is a densely distributed area of geological disasters such as debris flow. In August 2020, due to the stimulation of heavy rainfall, a large-scale group debris flow disaster occurred in Wudu section of Bailong river basin, causing serious losses. This paper takes the Wudu section (Lianghekou Township, Dangchang County to Jugan Town, Wudu District) of Longnan City in Gansu Province as the research area. Through field investigation, we selected the area of drainage basin, shape coefficient of basin, average slope, density of gully, reference value of material source (HI), lithology, distance between basin center and active fault, one hour maximum rainfall and vegetation coverage as debris flow hazard assessment factors. Taking single gully and small watershed units of debris flow as evaluation units, the regional debris flow hazard assessment is carried out by using ArcGIS software based on the theory of disaster entropy. The results show that most of the debris flows in the study area belong to medium and high hazard debris flow gullies. Some of the most heavily weighted disaster-causing factors like the weight of lithology, source reference value (HI), distance from fault, vegetation coverage and average slope are consistent with the actual investigation results. Moreover, the evaluation results of small watershed units are more consistent with the development of debris flow in the study area.