Restrained by flood limited water level, most reservoirs in North China discharge a substantive amount of water in order to vacate storage at flood season, while leaving little water for storage during post-flood season. As a consequence, a substantial part of storm-flood resources can’t be utilized adequately. Based on analysis of drainage area, this article divides the whole flood season into different stages, and thus conducted risk benefit analysis on dynamically raising the limited elevation of reservoir under the premises of guaranteeing dam body safety and downstream flood control security by mathematical statistics and multi-scheme, multi-level analysis. And finally the risk and benefit level of different limited elevation schemes is provided. Through the study on limited elevation of reservoirs during different stages of the flood season, this paper demonstrates the feasibility and necessity of increasing the limited elevation of reservoirs to resolve the water shortage in North China.