The rump of Xiangjiang River is located in Dongting lake district,which is river & lacustrine facies,and the hydrological changes are complicated.To explore the change of low water level in the rump section of the Xiangjiang River,we carry out an analysis from multiple factors such as the impoundment of the Three Gorges Reservoir,the construction of the upstream water conservancy project in the Xiangjiang River,as well as the sand mining in the lower reaches of the river.After impoundment of the Three Gorges Reservoir,the water level of Dongting lake outlet（Chenglingji hydrologic station）was slightly elevated,but that of the upstream Xiangjiang River decreased.Under the Changsha junction,there is no overall cut of riverbed.Although the coming sediment produced by three inlets and four branches of the lake year by year,it is significantly less than the amount of sand mining.The study result indicates that，the main reasons for constant slice of low water level in the Xiangjiang River trail reach lies in the large-scale sand mining in the river channel,which greatly destroys the riverbed form,thus not only seriously affects normal transport in the Xiangjiang River trail channel and threatens wading buildings’ safety,but also causes much destruction to the ecological environment.It is necessary to strengthen the scientific planning and management of sand mining in the Dongting Lake.