Abstract: In this paper a normal principle of the river system is introduced.Based on the analysis of water-sediment model of single reach,a numerical model for calculation of normal river system is established and tested with the observed data of the Jingjiang River and the Dongting Lake. The result shows that the computed data and the observed data fits well,which indicates that it is suitable to describe the complex boundary of the Jingjiang-Dongting,and the model is applicable.