Abstract: The human activity and climate change have significantly altered the river flow and spatio-temporal distribution of flood process, which directly impact on design flood in the downstream section. The effects of upper reservoir construction and regulation on downstream hydrologic regime are reviewed, the main research contents of design flood theory and method in cascade reservoir operation period are proposed. We mainly discuss non-stationary flood frequency analysis method and the most likely flood regional combination method based on copula function, and compare their practicability. We recommend using design floods and flood control water level in reservoir operation period, and suggest further research references and directions.