Abstract: In order to test the effect of aerobic denitrification of Bacillus on activated sludge mixed bacteria system, using Bacillus subtilis as the additive of activated sludge (abbreviation as Bacillus activated sludge) as the main body of the study, it was found that the nitrogen removal rate was high under aerobic conditions.Then the aerobic denitrification characteristics of the sludge under different nitrogen sources(sodium nitrate and sodium nitrite) and different dissolved oxygen mass concentrations(0.6~2.5 mg/L) was studied by experiments, and the kinetic analysis of reaction was conducted. The result shows that the Bacillus activated sludge has characteristics of aerobic denitrification, and it can only reduce the nitrite nitrogen without reducing the nitrate nitrogen under aerobic conditions.Additionally, the effect of aerobic denitrification decreases with the increase of dissolved oxygen.The high rate of denitrification was found in anoxic stage as a rate of 12.45 mg/(g·h), while the maximum aerobic denitrification rate in aerobic stage achieved 50% of anoxic stage, and decreased with the increase of dissolved oxygen.