Abstract: Data of 435 years records of flood and drought disasters during 381-1949 A.D. in the Poyang Lake basin are collected in this paper. The drought and wet history periods  are divided and the start and end times of each period are also determine. The classification of flood and drought disasters are scientifically divided, then the corresponding  Moisture Index value is also determined based on historical information carried by the record. The mean value and variance of the Moisture Index in each wet and dry period from  960 to 1949 AD. are calculated improving the PⅢ frequency curve fitting method. The variations characteristics of the historical flood and drought disasters have been  studied. The research showed that there were three periods of wetnessdrought in the period of 960-1698 AD., then on there were over 250 years of wet and cold climate. During  the wet period,the numbers of serious flood year is much mone than the numbers of serious drought year. During the drought period,the numbers of drought years was slightly more  than the numbers of flood year,but the numbers of serious drought year is more than the numbers of serious flood year.
Key words：climate change；flood and drought disasters；history records; change characteristics；Poyang Lake