Abstract: There are approximately 66 tributaries in the Three Gorges Reservoir (TGR) area, and obvious sediment deposition has been observed in most of the tributary estuaries since the impoundment of TGR. Sedimentation leads to formation of entrance bars at the estuaries, bringing a possible adverse effect to the storage capacity of TGR and the navigation in the tributaries. This paper analyzes the sedimentation in river mouth regions and its main causes, focusing on the case of the Xiangxi River tributary. The results show that in the period of 2006 to 2011, the silted sediment in a 6.6 km long reach of this tributary mouth amounted to a volume of 241?104 m3, revealing a sedimentation rate larger than that of the Yangtze mainstream nearby. And from the initial TGR impoundment in 2003 to 2015, the thalweg was significantly elevated by 7 m on average over this reach and 12 m at maximum at the mouth. Most of the sediment silted in the Xiangxi mouth came from the section of Yangtze mainstream affected by the TGR backwater. The sedimentation rate will alleviate as the sediment from the upper Yangtze or Xiangxi shows a decreasing trend.