After domesticating activated sludge to enrich aerobic denitrifier, 105 strains were isolated from it. 25 strains with over 50% of TN removal rate were screened by measuring TN. It was proved that they can produce nitrate respiration under aerobic condition by measuring the concentration of NO2(-) -N , NO3(-) -N and N2. The denitrification process of the 24 strains is NO3(-) -N -->NO2(-) -N --> N2. Moreover, it was found that there were no obvious competition function between NO3- and NO2-. It is deduced that aerobic denitrification can help to realize shortened simultaneous nitrification and denitrification and nitration speed is more rapid via feedback effect.