This paper choosen the typical Karst area as the study area， and divided the study area into small watersheds， which based on digitalelevation model （DEM） and remote sensing image and field investigation. Based on the specific environment and disaster mechanism of the geo -logical disaster in the Karst area， this paper analyzed the contribution of soil erosion to the debris flow disaster in the karst area ， and put forwardthe calculating method of debris flow source of quantity. According to the formation conditions of debris flow and based on the watershed unit ，this paper choose seven evaluation factors such as the soil erosion， erosion of provenance， relative elevation， longitudinal slope， gully density，average slope of the formation area， channel bend coefficient， and used Analytic Hierarchy Process to determine the weight of each evaluationindex， and made the sensitivity evaluation of 17 debris flow in the Ertang River Basin of the study area. The evaluation results can reflect the spa -tial distribution and regional activity characteristics of debris flow disasters in Ertang River Basin ， and provide a scientific basis for the preventionand control of debris flow hazards and rational land use in small watershed.