[Objective] The risk of debris flow in Ya'an City was evaluated to provide scientific basis for predicting and dealing with debris flow scientifically and reasonably. [Methods] Firstly, a quantitative-hierarchy factors assessing system, including nine factors of three categories, was established. The factors were weighted by method of analytic hierarchy process(AHP). Finally, assessment model of hazard was applied to the spatial overlay analysis and took debris flow hazard division in Ya'an City. The division map of debris flow hazard included low-risk zone(I), risk zone(Ⅱ), high-risk zone(Ⅲ)and higher-risk zone(Ⅳ). [Results] Baoxing county had the lowest risk, only 8.8% was covered by Ⅳ zone.Risk of debris flow in Tianquan County was determined as fairly low as well. About 20.0% of Yucheng, Lushan, Mingshan County are covered by Ⅳ zone, and the two counties have moderate level risk. Risk of debris flow in Yingjing and Hanyuan County is fairly high, Ⅳ zone covered 45.0% approximately. The debris flow risk in Shimian County hits the top. The percent of Ⅳ going up to 57.4%, and the percent of Ⅲ up to 24.4%. [Conclusion] The capacity of debris flow disaster should be enhanced in prevention of Ⅳ grade risk, be alert to the potential danger in Ⅲ. The measures have monitoring, weather forecast, tree and grass plantation.