Abstract: Denitrification is one of the important processes of wastewater treatment plant (WWTP). The carbon source, reflux ratio, DO and agitation method are all important factors affecting the denitrification. Fifty-eight WWTPs in Taihu Lake Basin were evaluated for upgrading operation, and the law of water quality fluctuation, process design and equipments were investigated and analyzed to explore the impact of different conditions on the denitrification rate of activated sludge, so as to provide basic data for the operation and management of high standard WWTPs in the future. The results showed that the denitrification rate was in the range of 0~5.18 mg NO₃^--N/(g VSS·h), among which the average denitrification rate was 1.40 mg NO₃^--N/(g VSS·h). The main reason for the low denitrification rate was the low concentration of carbon source in the influent. Among them, the type and location of the added carbon source had greater impact on nitrification and denitrification. It could also enhance the denitrification performance of sludge through adding appropriate carbon source and sufficient stirring conditions. When adding easily degradable carbon source in the influent of each WWTP and maintaining a relatively low concentration of carbon source in the influent, the denitrification potential was found to be 1.16~20.80 mg NO₃^--N/g VSS·h at a high agitation rate, which indicated that improving the quality of influent water and creating better denitrification conditions were conducive to the improvement of the overall denitrification level. Setting proper internal reflux ratio could effectively enhance the biological denitrification performance, however, high dissolved oxygen in internal reflux had greater effect on denitrification, and reducing the reflux dissolved oxygen could effectively promote the NO₃^--N removal.