Abstract: Debris flow prevention priority (DFPP) is a part of debris flow mitigation priority (DFMP). DFMP is defined as in a given area and a period of time, the degree of priority for reduction of debris flows should be considered. DFMP is the sum of DFPP and debris flow relief priority (DFRP).Hence DFRP is an important component for hazard assessment.DFPP is directly related to regional hazard degree of debris flow, population density and regional development index. It is quantitatively expressed asP＝H×E×M where P is DFPP(10 000 yuan/km²);H is regional hazard degree of debris flow (0-1);E is population density (person/km²);M is per capita GDP(10 000 yuan/person).H is a function of twelve variables relevant to natural characteristics of debris flow. The primary factor is distribution density of debris flow, the secondary factors are involved in environmental background, including geological, geographic, meteorological and climatic factors. Detailed findings are available in previous researches.E indicates the importance of people in the given region. The more the population density, the more important the region. M represents the situation of development in the region. The higher the per capita GDP, the more developed the region, and the more worthy to be prevented from natural hazards.Practice of this method in Aba Prefecture of Sichuan Province has demonstrated that it is significant and feasible. Assessment of DFPP could provide scientific references and decisions on debris flow management and master plan for policy makers of government agents. Furthermore, assessment of DFPP could provide assessment model for other kinds of natural hazards, so as to more widely popularize this methodology in the other parts of China.