Abstract: At present, the widely used method of regional debris flow hazard assessment was proposed by Liu Xi-lin. Because the method is based on administrative region as assessment unit, it does not reflect the geomorphic conditions of debris flow, and it is difficult to get some assessment indexes. Based on watershed unit, the article establishes the assessment system of debris flow. According to the topographic conditions, source conditions and hydrodynamic conditions required for the formation of debris flow, the factors related to debris flow source, channel and rainfall are selected and assigned as the assessment index, which are analyzed and evaluated using GIS technique. Taking the Dadu river basin as an example, according to the development characteristics of debris flow, relevant factors and indexes are selected to evaluate debris flow hazard; the evaluation results are in accordance with the actual situation, which is helpful for planning to reduce the damage by government.