Through the measured survey data of the water quality of a river in Shanghai, the space-time distribution characteristics of eutrophic pollution factors in river water were analyzed, and the eutrophic pollution degree of the water body was evaluated by the comprehensive nutrient status index method. Results show that the river water quality indexes of Chla, TN, and COD_Mn all presented high values in summer and low values in winter, while SD was high in winter and low in summer, and TP did not change significantly with the seasons. The water pollution was the most serious in July. Both the average concentrations of COD_Mn and TN in the water body were about 2 times higher than the water quality standard of class V. Chla and SD were at the inferior class V level, and TP was at the class V level. The river water was seriously polluted by nitrogen and organic matter. The water body mainly presented mild eutrophic state in winter. In spring and autumn, the water body was mainly in moderate eutrophic state. Severe eutrophication occurred in the segment 4～6 of the river in summer (June). From July to August, the water body presented severe eutrophication, and the eutrophication bloom of the whole river was prone to burst out. Controlling the discharge of exogenous pollutants, strengthening the monitoring and evaluation, and forecasting eutrophic state of the river water were the keys to control the black smelly eutrophication of river water and realize urban water clarity.