Excessive nitrogen loading has been regarded as one of the most important factors causing eutrophication of lakes. The traditional views show that when nitrogen deficiency occurs, lake ecosystems can obtain nitrogen from the atmosphere through biological nitrogen fixation to meet their nitrogen needs, so according to this assumption, the main limiting factor of the primary productivity of water bodies is phosphorus availability. However, recent research has shown that nitrogen fixation does not meet ecosystem demands, and nitrogen or nitrogen and phosphorus limitation are generally accepted. Furthermore, eutrophic lakes often exhibit nitrogen limitation, meaning that they are sensitive to additional nitrogen inputs. In this paper, research on the polluting effects of nitrogen in Lake Taihu was reviewed. Both the internal and external loadings of nitrogen to the lake were considered. The nitrogen inputs from the three main sources, i. e. input from rivers, precipitation from atmosphere and release from sediments, were analyzed. The results show that there is obvious spatial heterogeneity in nitrogen pollution of Lake Taihu. The pollution is relatively heavy in the western and northern parts of the lake and relatively light in the southeastern part. River input is a major source of nitrogen loading to the lake. Internal loading is also an important source of nitrogen pollution. However, to release a quantity estimate is mainly based on the amount of sediment resuspension, and about the release quality, how many percentage can be used by phytoplankton is still not clear, especially the particulates mineralization rates. The cycling nitrogen in lakes mostly mediate by nitrification, denitrification, nitrogen fixation and anammox. In Lake Taihu, the process of biological nitrogen fixation has been found to contribute little to the total annual input of nitrogen and denitrification is the main process through which nitrogen is removed from the lake.