Ecological stoichiometry is an important measurement to evaluate water trophic status. In this study, the ratio of nitrogen to phosphorus (N/P, an index of stoichiometry) was used to assess the nutrient conditions of Tiaoxi River which is the main inflow river of Taihu Lake. The results from field monitoring data showed that nitrogen contents in Tiaoxi River were much higher than surface water quality standards in China but phosphorus pollution was relatively light. The average concentration of total nitrogen (TN) was up to 3.5 mg/L, which was worse than Grade V (2mg/L) of national surface water quality standards in China, while the average concentration of total phosphorus (TP) was 0.18 mg/L, which met the water quality requirement of Level Ⅲ (0.2 mg/L). In addition, nitrate and particulate phosphate were the main pollutants in Tiaoxi River. The average content of nitrate was up to 2.1 mg/L, indicating that Tiaoxi River was in a high oxidation environment and its self-purification ability was strong, whereas the mean value of dissolved phosphate (DP) was low (0.07 mg/L). Nutrients concentrations presented the similarly seasonal variations. The maximum concentration of TN was in winter, and the minimum level was in spring and autumn. The dynamic changes of TP concentration were roughly similar to TN, but TP presented a sharp decline in spring and fell to the lowest level throughout the year. Furthermore, correlation analysis also showed certain correlations among different nutrients index. TN and TP, DP were significantly positively correlated, indicating that the ways for nutrients inputs to Tiaoxi River were substantially the same, which suggested that Tiaoxi River was mainly influenced by agricultural non-point source pollution. TN/TP ratio represents the nutrients structure in Tiaoxi River for phytoplankton growth. According to the previous studies, TN/TP<7 and TN/TP>30 were used to categorize the different trophic status of nitrogen and phosphorus limitation in aquatic ecosystem, respectively. The N/P ratios showed that Tiaoxi River in spring and autumn (TN/TP>30) were under the condition of phosphorus limitation. It was demonstrated that the water was suitable for algae growth in summer (730), and linear regression showed that N/P ratio was mainly affected by phosphorus fluctuations. In the inlets of Taihu Lake and some other dead water zones, the TN and TP concentrations were higher than 0.80 mg/L and 0.20mg/L, respectively, and the water flow velocity was slow, thus dominant bloom-forming cyanobacteria was not limited by nutrients content. Consequently, the TN/TP ratio, absolute nutrients concentration and water flow status were appropriate to meet the requirements of algal bloom. By researching and analyzing the whole river, it was concluded that the algal bloom risk in main stream of Tiaoxi River was lower than in part tributaries and dead water zones, which would significantly increase the algal bloom risk in the inlets zones of Taihu Lake, especially in summer. Furthermore, some strategies for water quality improvements were proposed based on the eutrophication status of Tiaoxi River.