Abstract: Flash flood disasters investigation and assessment includes analyzing and calculating of design flood, current flood control capacity and early warning indicators. It is a foundational element for flash flood disasters forecasting. However, most flash flood prone regions locate in small watershed, and there are no runoff records. The design flood is generally obtained by theoretical analysis, and some parameters may differ from reality. In this paper, based on first hand survey data from flood disasters at Waxi-River in Gucheng Counter, the relationship between the water level and flow rate in the flash flood disasters assessment results is verified; the applicability of the calculation method of design flood and the rationality of relevant parameters are discussed. The critical rainfall and early warning indicators are also analyzed. This study is expected to reach the objectives include adjusting relevant parameters, completing the current evaluation system and enhancing the accuracy of the early warning indicators. Meanwhile, this method provides reference value to review of flash flood disasters assessment in the data-lacking area.