Dam break can cause disastrous consequences to natural, economic, and social systems in the downstream area. A nalysis of vulner ability to dam-break disaster helps develop measures of mitigating disaster losses. This paper presents a quantitative method for evaluating vulnerability of dam-break disaster based on data envelopment analysis method with the downstream area of Huaxi dam as an example. Results show that Xiaohe District and Nanming District have high vulnerability, Huaxi District has middle vulnerability, and Yunyan District has low vulnerability in the study area. The study also provides some reference values for developing measures of mitigating disaster losses.