Hongze Lake plays an important role in flood control in the Huaihe River Basin. At present, there are only a few incomprehensive studies researched on the regulation and storage capacity of Hongze Lake. The process of flood regulating and storing of Hongze Lake was combed, and the flood regulation and storage function of Hongze Lake was divided into storage and detention function and regulation function in this study. The flood regulation and storage capacity was analyzed based on the data of rainstorm and flood in 1991, 2003 and 2007. Hongze Lake has little change in the amount of flood storage, which is about 30×108 m3, showing a increasing trend. The reservoir volume can not fully represent the storage and detention function of Hongze Lake. The adjustment coefficient, which can represent the effect of the lake on flood storage more accurately, is proposed. The adjustment coefficient of Hongze Lake increased from 0.19 to 0.21 to 0.38, indicating that the effect of Hongze Lake on flood storage and detention is gradually strengthened. The regulation effect of Hongze Lake on the high-lean flood and the short-fat flood is obviously different, and the regulation effect on the short-fat flood is stronger. It is pointed out that the discharge capacity of the outlet channel is also a part of the regulation and storage capacity of Hongze Lake, and the application of artificial river plays an important role in flood control. Sediment deposition and artificial reclamation are the decisive factors affecting the flood regulation ang storage capacity of Hongze Lake. The research results provided theoretical guidance and technical support for the analysis on flood regulation and storage capacity of Hongze Lake.