Global climate change causes frequent extreme rainfall and mountain torrents are becoming the main natural disasters in the world. In this study, mountain flood disasters in the small watershed of Xiuyanhe River in Zichang County were selected as the research object. Based on the characteristics of small watershed, social and economic conditions, meteorological and hydrological data, the flood control capacity of the villages and towns in the flood-prone area of the small watershed of Xiuyanhe River in Zichang County was evaluated, and the disaster zonalization, warning index and threshold were determined. To provide basic information and technical support for mountain flood monitoring and early warning and disaster prevention and mitigation in Zichang County. The whole work adopts the design rainstorm flood calculation, and takes the small watershed as the basic unit, calculates the design rainstorm, deduces the design flood, analyzes the flood control capacity, determines the early warning index, and evaluates the mountain flood disaster risk level of each flood control object.