According to the annual highest water level records by historical documents (1736-1991) about Hongze Lake, as well as the data of water level and discharge at hydrologic stations around Hongze Lake (1914-1992), this paper makes frequency analysis of various flood parameters in long and short time courses, calculates designed in-lake flood volume in return periods, and analyzes return periods and flood damage which corresponds to the flood years. The results show that;(l) Floods occured frequently in history in Hongze Lake, when serious floods took place in the years of 1786, 1851 and 1906, and water level of Zhizhuang at Gaoyan reached up to 16.3, 23.4 and 16.1 Chi respectively:(2) After Hongze reservoir built in 1953, the lake water level went up. The yearly highest water level increased by 1.22m while the perennical mean water level increaead by 1.72m; (3) The frequency analysis results on peak discharges, maximum 3-day flood discharge as well as annual mean discharge, respectively at Bengbu hydrological station in Huaihe River (1914-1992) show that the flood in 1954 wa's equivalent to 20-year. 5-year, 45.5-year and 30.0-year peak flood discharges while the flood in 1991 was equivalent to 7.1-year, 7.1-year, 10-year and 14.7-year peak flood discharges, respectively. Different frequency analysis results show that the flood discharge in 1991 was less while the damages in 1991 were greater than those in 1954.