Abstract: In recent years, there are more and more researchers who conducted studies on the Poyang Lake about the water and sediment transport. However, they mainly focused on statistical analysis of water and sediment data at five hydrologic stations on the Ganjiang River, Fuhe River, Xinjiang River, Raohe River, Xiushui River. The data were obtained from 1956 to 2005 and the missing data were not interpolated in those researches.In this study we took the variation characteristics of runoff and sediment transport of the Poyang Lake as a whole. Studies of water and sediment transport characteristics provide evidence for researching the change in the morphology, and could give reasonable guidance in exploitation and utilization of soil and water resources in the Poyang Lake. Firstly, we used two methods to interpolate the lack of measurement data in the Poyang Lake from 1956 to 2011. Secondly, the variation characteristics of runoff and sediment transport at important hydrometric stations of the Poyang Lake were analyzed by using mathematical statistics, the double accumulative curve of annual runoff and sediment and the Mann-Kendall method, based on the data from 1956 to 2011. Then we studied the causes of the variation characteristics of runoff and sediment transport in recent decades. The results showed that: 1) The annual distribution of runoff into the lake was consistent with sediment load, however, the phenomenon of the Yangtze River water and sediment flow backward influenced the annual distribution of runoff and sediment transport out of the lake; 2) The trend of the annual variation of the suspension sediment load into the Poyang lake began to intensively decline from the 1990s, but the suspension sediment load out of the Poyang lake presented a whole descending trend from 1956 to 2000, the data also demonstrated that the suspension sediment load out the Poyang lake is on the increase from 2001 to 2011; 3) Sediment load into the Poyang lake appeared to be a mutation point around 1998, sediment load out of the Poyang lake occurred around 2003. 4) Change of runoff transport tended to be a relatively stable state in the 56 years, but in recent decades, it has close relationship with the influence of the precipitation in the Poyang Lake basin. Then change of sediment transport of Poyang Lake is relatively complicated. Sediment load into the lake was significantly reduced, but sediment load out of the lake increased obviously. The reasons caused reduced sediment load into the lake include: ① There were many reservoirs in five rivers of Poyang Lake, which had function of water storage and sediment retaining, such as Wanan reservoir. ② The government strengthened soil and water conservation in the Poyang lake basin so that this measure can obviously decrease sediment load. ③ The downstream of the five rivers were infected by the sand-excavation on the river channel, which led to reduced sediment load into the lake. However, there were many reasons which induced increasing sediment load out of the lake: ① The depth of river bed was decreased in Hukou. ② Influenced by the Three-Gorges Project, gradient ration about the Poyang Lake and Yangtze River was increased. ③ Sand mining could cause the disturbance of the river bed so that the river flowing velocity became faster.

Key words: Poyang Lake, runoff and sediment characteristics, the evolution tendency, mutation analysis