Abstract: Through field investigation of Datong Lake polders and in the combination with river-lake connection planning and scheme, aiming at the connection scheme of water diversion from Caowei River to East Dongting Lake, a coupled water quality model of DYNHYD and WASP is established. After the determination of model parameters, the model is used to calculate and simulate TP variation of Datong Lake and the main river channels under the condition of typical dry hydrology year. The analysis and simulation results show that in typical dry year, 135 days are need for TP content to reach the required classification III water of the Datong Lake, however the corresponding time in rivers is significantly longer. The analysis and process can provide reference and practical guidance for application of the coupled model water quality of DYNHYD and WASP in southern complex river network area.