Cascade reservoirs design flood calculation is based on the situation reservoir downstream from the bottom layer by layer analysis and calculation,by way of example two reservoirs of cascade design flood for analysis in the paper，in general, the design flood of the downstream reservoir is consists of the discharge process of the upstream reservoir and flood intervalbetween two reservoirs,but also need to specific analysis on the upstream reservoir spillway changed the natural flood situation and the influence on the degree of the downstream， Focus on the analysis of the influence of flood regulation and the regional flood of the upper reaches of the reservoir,regional flood composition of interval flood,and select the appropriate calculation method.It can provide a useful reference for the calculation by cascade design flood analysis and thinking of the ways.