Even if a pumping station, which is a representative structural flood defense facility, operates optimally, flooding occurs at certain nodes in the drainage area. In other words, even if rainwater pumping stations and rainwater storage tank, which are structural flood defense measures, operate at maximum, it is necessary to review areas where overflow occurs. Therefore, in areas where it is impossible to protect against inland flooding using structural flood defense measures alone, new flood defense measures are required. In this study, based on previous research on rainwater pumping station operation techniques to reduce critical flooding, the Daelim 3 region was divided into 45 basic areas and vulnerability analysis techniques were applied to select the location of rainwater storage tank for effective flood defense. A possible technique is presented in this paper. As a result of the study, sub-region 1 had the highest impact index value, so installing a rainwater storage tank was calculated to be more effective in preventing floods than installing a rainwater storage tank in other sub-regions. The priority-estimation technique for flood defense facilities presented in this study can be effective in establishing plans for flood control structures other than rainwater storage tank.