Variations of water and sediment of Jinsha River have important impact on incoming water and sediment condition of Three Gorges Reservoir. This paper analyzed the water and sediment characteristics upstream Ertan Reservoir. The method of multiple regression analysis was used to evaluate the sediment trap of the Ertan Reservoir. The siginficant analysis result showed that the regression models were all significant. The calculated results showed that during year 1998 to 2004, the annual sediment trap of Ertan Reservoir is about 5000～6500×104 t, and the Reservoir deposition rate is larger than 0.66％.From year 2001 to 2004, the sediment trap of Ertan Reservoir diminished to about 4000～5000×104 t due to the decrease of the incoming sediment upstream Ertan Reservoir. It is about 95%of the sediment coming from the upstream deposited in the Reservoir. Compared to year 1991 to 2000, the sediment trap in 2001 to 2004 is added about 0.238×108 t. It is contributed about 21.25% to the total sediment decrease of the Jinsha River basin. According to the way of Ertan Reservoir deposition and the current water and sediment condition, after the construction of the cascading reservoirs of Jinsha River and Yalong River, these reservoirs could trap about 90% of the incoming sediment, and the incoming sediment of Three Gorges Reservoir may decrease more than 60%.
