The invention discloses a hydropower-station flood optimization dispatching method which takes gate operation rules into consideration. The method includes five steps: (1) structural description of the gate operation rules, which solves an expression problem of the complex gate operation rules; (2) instantiation of the gate operation rules, which solves a problem of how to use the structural-body examples of the gate operation rules to describe specific hydropower-station gate operation rules; (3) optimization generation of a gate opening combination number sequence, which solves a problem of coupling of the gate operation rules and traditional hydropower-station flood optimization dispatching methods; (4) optimization adjustment of the gate opening combination number sequence, which solves problems that in a flood dispatching process, during specific periods, water level exceeds the limit and at the end of a dispatching period, deviation exists between the water level and a target water level; (5) generation of a gate operation plan, which solves a problem of generating the gate operation plan dynamically according to the gate opening combination number sequence. The hydropower-station flood optimization dispatching method which takes the gate operation rules into consideration improves prediction accuracy of a later-period flood-discharge flow process and improves the rapid response capability of a flood prevention decision of a hydropower station.