Based on precipitation data of 52 meteorological stations in Hunan province from April to September during 1958～1998,the flooding years are determined,the features and evolution trends of flooding in the last 40 years are analysed.The causes of increasingly serious of the damage in recent years are studied on the basis of above discussion.The climatic background, the unusual atmosphere general circulation,the influence of ElNino,the specific property of hydrology and area rapid reduction of Dongting Lake and elements of society are the influential factors.