Abstract: In order to evaluate the relationship between rainstorm and deposited flood of reservoir and provide the theoretical basis for removing danger and reinforcement of the large and small reservoirs in the southern mountainous area of Tongliao, the relationship of rainstorm and flood process daily was calculated by a simple approximate method, the author took the example of the largest medium-sized reservoir (Kong Kong reservoir). The results showed that: there was something about daily rainstorm and daily deposited flood of reservoir. The maximum flood peak discharge was calculated based on flood frequency. It had important guiding significance under the condition of lacking of information in the feasibility study stage or removing danger and reinforcement of the large and small reservoirs.