Based on theory and method of multi-grade fuzzy evaluation in fuzzy mathematics, combined with the characteristics, cause and mechanism of debris-flow hazard,the paper set up a new multi-grade fuzzy evaluation model of debris-flow proneness and used grey correlation method to determine the weight of various impact factor.Taking Hanjiagou debris-flow gully of Jiudianxia reservoir for example,according to typical evaluation indexes,the paper established the secondary approximate reasoning and evaluated the debris flow liability by two-stage fuzzy comprehensive evaluation.The liability of debris flow can be divided into four levels, and the liability of debris flow of reservoir area was divided,which can provide the basis for the disaster prevention of reservoir debris flow gully.