Abstract: In order to explore the real effect on one denitrification reactor, a sewage treatment plant carried out some relevant tests.Three experiments were done at the same time in this plant, which were condition Ⅰ(just adding carbon source), condition Ⅱ(adding carbon source and denitrifying bacteria) and condition Ⅲ(adding carbon source and denitrifying bacteria after denitrification reactor treatment). The usage quantity of carbon source and bacterial agent were recorded. The total nitrogen removal rates in condition Ⅰ, Ⅱ and Ⅲ were 74.47%, 83.54% and 85.57% respectively. Combined with the removal rate of COD and TN, water inflow and carbon source dosage, the working condition could be calculated that 27.13mg/L TN could be eliminated by 177.08mg/L COD in condition Ⅰ.While in condition Ⅱ, 53.89mg/L TN could be eliminated under 180.5mg/L COD and 55.43mg/L TN could be removed by 177.0mg/L COD in condition Ⅲ. When in the same COD concentration, the TN removal rates in conditions Ⅱ and Ⅲ were higher than condition Ⅰ. The TN removal rate of condition Ⅱ was slightly lower than that of condition Ⅲ, but the use of bacterial agent dosage was 10 times higher. Above these experiments, the effect research of intelligent denitrification machine got a conclusion that the denitrification machine could reduce the amount of denitrifying bacteria and maintain high efficiency of denitrification.