Abstract: An unsteady water quality and hydrodynamic model for river networks was employed in computing the amount of pollutants passing through the four east outlets in Pearl River delta into Lingding sea.The computed area is about 2000 square kilometers.Based on the verified model and the long series of the water quality data observed of 1985-1995 in the four east outlets,the amount of pollutants into Lingding sea are calculated and its variations are analyzed.The main conclusions are that the main pollution factors are COD and NH₄,and the main pollution outlet is Humen.The 2-D hydrodynamic and water quality model is used to calculate the water quality in Lingding sea area which is influenced by Pearl River delta and Hong Kong pollutant.The model is calibrated and verified with the real data.The main conclusion are as follows: (1) If the water quality in east outlets is satisfied with the desired function and the water quality in Lingding sea can not reach the desired function.(2) The pollutant discharged by Hong Kong only influence Shenzhen bay even though in unfavorable hydrological conditions.(3) The water quality is higher in northwest of Lingding sea because the along shore flow is toward northwest.(4) If the pollu tion accidentlly occur in east outlets,the influenced area is at middle area in Lingding sea.