Abstract: The existing reservoir water-supply operation rules focuses on the single water supply,paying little attention to multipurpose water supply with different priority and reliability.This paper proposes a reservoir operating rule for the multipurpose water supply,which can deal with the different water supply respectively,make sure no severe shortfall happens and achieve the operating objective of minimizing the total water-supply shortage.A model combining simulation and genetic algorithm is used to optimize the parameters of the proposed operation rule,and the genetic algorithm is proved to give good performance in searching the optimal parameter combination.The case study justifies this operating rule for multipurpose water supply.