The invention discloses a reservoir level control method under a circumstance of frequent flood in a flood season. The method comprises the following steps: S1, determining a first-level cascade reservoir section inflow amount in the flood season according to hydrometeorological information; S2, determining the upper limits of the cascade reservoirs; S3, calculating the last phase volumes of the cascade reservoirs; and S4, calculating the gross generation of the cascade reservoirs. In the cascade reservoirs, the reservoirs with certain adjusting capacities have different adjusting reservoir capacities in different water levels in different stages, and the abilities of flood diversion and storage are also different. By taking typical flood of the reservoirs with certain adjusting properties in the cascade reservoirs as an input, combining with different water levels in different stages in a scheduling graph of the reservoir as a adjusting start water level, and modeling cascade optimization as a target for adjusting calculation, cascaded generating capacity is calculated. The later stage water level of the reservoirs with the certain adjusting properties does not exceed a flood control limited water level or a normal high water level, thereby providing more selections to scheduling operation of the cascade reservoir and providing a policy support for optimal operation.