The result of analysis of the weather causes of the aggravated of drought and flood disaster in Dongting Lake Region based on statistic analysis of some indices and the meteorological observation data of Dongting Lake Region,the Four River basin in Hunan,the upper reaches of the Yangtze River show that the wet and dry of rainwater resources in Dongting Lake Region is directly influenced by interdecadal variations of the location of mainbelt in China. Further it influenced the tendency of waterlogging-drought variation. Then it influenced the tendency of waterlogging-drought variation. The East Asian summer monsoon and sea surface temperature in the central and eastern equatorial Pacific effected the location of main-belt in China then influence the wet and dry of rainwater resources in Dongting Lake Region. Rainwater resources in Dongting Lake basin synchronously wet or dry under the background of climate warming,which trend to result the flood pile up in Dongting Lake or lead to the origin of water resources exhausted. The increased of the water resources of Dongting Lake Basin at the dry season aggravated the water shortage level.