Abstract: In recent years, the interference of large-scale agricultural nitrogen fertilizers and fossil fuel has increased the nitrogen input into the ecosystem, leading to environmental problems such as excessive nitrate content in rivers, eutrophication of lakes, reservoirs, and nearshore waters, and soil acidification. The Yangtze Estuary and Hangzhou Bay are the primary zones where water quality has dropped to Class Ⅳ (Sea Water Quality Standard (GB 3097-1997)). As one of the important rivers flowing into Hangzhou Bay, the total nitrogen concentration and flux of the Yongjiang River have increased significantly in recent years. The current estimation of nitrogen budget in the river basin is of great significance and guidance for carrying out nitrogen pollution control and management in the basin and improving water quality in the nearshore waters. The basic statistical data and related parameters of the river basin in 2021 were collected and used to estimate the nitrogen balance. The main driving factors of nitrogen balance and their impact on the environment were clarified. The results show that the nitrogen input in the Yongjiang River Basin in 2021 was 51,060 t and the nitrogen surplus was as high as 21,730 t, accounting for 42.56% of the nitrogen input. The average nitrogen load in the watershed (172.56 kg/(hm²·a)) and land nitrogen flux (105.8 kg/(hm²·a)) were both higher than the national spatial scale average. The main sources of nitrogen input included human and animal excretion, chemical nitrogen fertilizer, and atmospheric deposition, accounting for 39.11%, 26.33% and 20.91%, respectively. Among nitrogen output, 48% was taken away by crop harvest, 26.98% entered the atmosphere through denitrification and ammonia volatilization, and 21.47% entered the water environment in the form of runoff. From the perspective of spatial distribution, areas such as Yinzhou and Zhenhai faced a relatively serious potential risks of nitrogen pollution. Redundancy analysis (RDA) showed that population density, population size, crop planting area, livestock and poultry number, the total output from the industrial enterprises related to human activities, urbanization level and GDP were the main driving factors of nitrogen excess, nitrogen load, as well as the land nitrogen flux in the river basin. In view of the serious excess of nitrogen, it is recommended to adopt nitrogen source reduction and related control measures to eliminate the negative impact of excess nitrogen on the nitrogen balance in the watershed. The studying can provide scientific basis and support for further formulation of nitrogen pollution control measures, scientific regulation of nitrogen process in the basin, and improvement of water environment quality in nearshore waters.