Abstract: Base on the survey results of flash floods for a small watershed in Huangshan City of Anhui Province, this paper inspected the reliability and rationality of the survey results of flash floods disaster in the field. The characteristics of rainstorm-flood in river basin, the degree of flood impact and the current ability of flood control were analyzed and evaluated. The rainfall thresholds were calculated in different antecedent precipitation index. This study also analyzed the rationality of rainfall thresholds. According to the characteristics of rainstorm-flood in river basin and the non-structural measures of flash floods disaster, adopting characteristic time-interval rainfall for early warning and setting up additional automatic measuring rainfall stations in river basin are recommend.