Based on the monthly monitoring data of Lake Hongze from 2010 to 2019, the main pollutant indicators including total nitrogen (TN) and total phosphorus (TP), which affect the water quality of Lake Hongze, were studied. 25 main inflow rivers and 2 outgoing rivers around Lake Hongze were selected for monitoring from October 2019 to September 2020, and the impact of exogenous river input on lake nitrogen and phosphorus in different lake regions and their water period variation rules were discussed. The results showed that:(1) the concentration of TN and TP in Lake Hongze remained in a high level for a long time. The annual average concentration of TN and TP fluctuates in the range of 1.39-1.86 mg/L and 0.080-0.171 mg/L, respectively. The temporal and spatial average concentrations of TN and TP in the main inflow rivers (1.92-5.70 mg/L and 0.114-0.181 mg/L) are higher than the lake in the same regions (1.15-1.46 mg/L and 0.088-0.101 mg/L). The concentration of TN and TP in Xiaohe River, Mahua River and Wuhe River, which are the main rivers that affect the concentration of TN and TP in Lake Hongze, is significantly positively correlated with that in the adjacent lake. Weiqiao River and Gaoqiao River near the southern regions of Lake Hongze are the main contributors of TN and TP during non-extreme rainfall period. (2) The water transfer project has a significant impact on the concentration distribution of TN and TP in the body of Lake Hongze and main inflow rivers. During the water transfer period, the TP concentration of the lake gradually increased along the water transfer direction, while the TN concentration showed a trend of first decreasing and then increasing. TN concentrations of the Weiqiao River and Gaoqiao River in the south reached the peak of the water period, which were 10.69 mg/L and 9.90 mg/L respectively. (3) The concentration of TP and TN in the inflow rivers during the extreme rainfall period is significantly higher than that in other water periods. Due to the different enrichment effects of lakes on TN and TP, TP concentration was high in the middle and low around it, while TN concentration showed a law of gradual decrease along the flood flow direction.