Abstract: Based on the water supply risk and its variable process of Dalian city, this paper proposes a cost-benefit analysis method for flood resources to inquire into the control range of the reservoir's flood limit water level, according to the use course of the flood resources and flood range analysis.The result of a case study demonstrates that the proposed flood limit water level of Biliuhe reservoir can go up suitably, along with the step by step raise of water supply.