Abstract: Nitrogen inputting through the rivers which enter into the Taihu Lake is one of the main sources of the nitrogen pollutants in the Taihu Lake. For the purpose of revealing the variation characteristics in the process of the rivers entering into the Taihu Lake and the potential reasons, the Caoqiao River, the South Tai-Ge Canal and the Dapugang River were chosen as the typical rivers in Jiangsu Province which enter into the Taihu Lake for a field investigation. Then, the variations of nitrogen components in the three typical rivers were analyzed based on the field monitoring data. The analysis results show that total nitrogen concentrations all rise along the rivers, although the components of nitrogen have their own variation characteristics. It is also found that the nitrate is the main component of nitrogen in the Caoqiao River and the South Tai-Ge Canal, and that the ammonia is the main component of nitrogen in the Dapugang River. Meanwhile, the reasons for the variation of nitrogen components are not the same. The crossing of rivers and the discharge of wastewater treatment plants can influence the nitrogen concentration in the rivers entering into the Taihu Lake. Therefore, when a river improvement plan is implemented, not only a pertinent strategy should be made, but also the influences of the river crossing should be taken into account. Besides, effective measures should be adopted to reduce the nitrogen concentration in the effluent of wastewater treatment plants.