Abstract: Luojin ditch, located in the outer edge of Detuo Township in Luding County, Sichuan Province, is connected with the bank of Dagangshan Hydropower Station. The existence of debris flow in Luojin gully threatens the safety of people's life and property and the operation of Dagangshan Hydropower Station. In this paper, using Luojin ditch debris flow as an example, I try Gray relational method to evaluate the danger of debris flow. The size, frequency, main groove length, watershed area, watershed cutting density, relative height difference, and unstable trench bed ratio was selected as evaluation factors. Concluded as follow:(1)Luojin ditch debris flow is rich in resources, the total amount of about 21.95104m3. The debris flow velocity is estimated at 5.33ms-1 and the debris flow peak flow is 487.3m3s-1. (2)The fall of the Luojin ditch debris flow is mainly controlled by the torrential rain. Its bulk density is estimated as 1.8tm-3. (3)According to the risk calculation, the calculated risk is equal to 0.45, and it is concluded that Luojin ditch belongs to moderate dangerous debris flow.