Abstract:According to the data of runoff of the Four Rivers(Xiangjiang River, Zishui River, Yuanjiang River, Lishui River)measured by main hydrological station during 1990—2013, we analyze the annual variation law of runoff in flood season of the Four River and conduct a gray correlation degree analysis over the distribution of indicators in the flood season and floods and droughts situation in Hunan Province with the methods of moving average, wavelet analysis, Mann-Kendall mutation test, non-uniformity coefficient and amplitude of variation, etc. The results indicate that: (1)the distribution of inter-annual flood season’s runoff into Dongting Lake from the Four Rivers was quite uneven, while the flood season’s runoff into Dongting Lake presented a trend of decreasing in general. (2)For Xiangtan station and Taojiang station, the first main cycle was 6 years; for Taoyuan station and Shimen station, the first main cycle was 4 years. (3)At Taojiang station and Taoyuan station, mutations occurred in 2003 and 2004, respectively. For Xiangtan station and Shimen station, there had been no mutation. (4)During the flood season, the distribution of runoff into Dongting Lake from the Four Rivers was quite uneven, however, the runoff distribution tended to be even over time. The monthly runoff showed a decreasing trend with fluctuation. As a whole, the indicators from the four stations presented a decreasing trend. (5)The grey correlation degree of the runoff distribution characteristics index value of Four Rivers into Dongting Lake during the flood season and river basin’s flood and drought disasters was extremely high, reflecting the situation of the basin’s flood and drought disasters.