By using the hydrological and topographical data collected from hydrological stations around Dongting Lake, the amount of sediment deposition and erosion from the lake(1956-1995) is analyzed with sediment budget method and topographical method. The results demonstrate that the inflow from the Lishi River, Yuanjiang River, Xiangjiang River and Zishui River contributes 57.8% of the total water into Dongting Lake, while the runoff from the Yangtze River through 4 intakes and channels which connect the Yangtze River and the lake occupies 33.6%.Among the sediment transported into the lake, 79.5% is from the Yangtze River, 18.2% from the four tributaries and only 2.3% from the local area.Up to 74% of the sediment into the lake is deposited in the lake, with the rest carried out of the lake to the Yangtze River. The runoff flowing from the Yangtze River into the lake has been reducing because of the siltation of the lake. Hence the siltation rate and the flow returning into the Yangtze River decrease. The total amount of sediment deposition in the lakes in the past 40 years (1956-1995) was calculated at 4.93 billion cubic meters that made the lake silled up by 0.63-0.74 m. The rate of siltation is estimated at 0.018 m/a¹ with the sediment budget method and 0.016 m/a¹with the topographical method. Sedimentation in the period 1983-1995 led eastern part of Dongting lake shrank by 1.5%, southern part of Dongting Lake by 2.5%, Muping Lake by 5.4% and Qili Lake by 22.5%.In the past 40 years, the East and West branches of the Songzi River, the lower reaches of the Zishui River, the Caowei River, the south and north outlets of Dongting lake have exhibited a bed degradation by 1.03m, 0.5m, 0.26m, 0.67m, 0.15m and 0, 52m respectively, whereas the rest have silted up. In the main outlet of the lake, Chenglingji Station, erosion has been observed since 1988.The impoundment of the Three Gorges Reservoir will probably reduce the inflow of water and sediment to lake and the rate of siltation of the lake will slow down.