According to the inflow and outflow, water quality data of Nanjing Sewage Treatment Plant and tap water consumption in 2016, the current situation of pollutants into the Yangtze river in Gulou District was analyzed. By constructing a one-dimensional steady-state water environment mathematical model, the relationship between pollution source and water quality was established, and the amount of pollutants into the river was verified. Under the condition that the water quality of the section of Sanchahekou at the Qinhuai River and the section of Pagoda Bridge at Jinchuan River has reached the standard，the water environmental capacity in the Gulou district is calculated. The results show that the water environmental capacity of COD is 21,798 t/a, NH3—N is 733.24 t/a and TP is 61.30 t/a. Combined with the actual situation in Gulou District, this paper puts forward two feasible measures to meet the requirements of two sections in terms of construction of drainage standard areas, treatment of black-odor river courses, upgrading of sewage treatment plants, and introduction of supplemental water, so as to provide a theory for environmental protection departments to further improve the water environment in Gulou District.