Abstract: To improve the denitrifying phosphorus and nitrate removal efficiency and availability of carbon source, the effects of influent COD and different addition methods of COD on the denitrifying phosphorus removal of A ²O-BAF were investigated. Different feed water ρ(C)/ ρ(P) ratios of 25-71 and three different addition ways of COD: one-time adding, three-time adding, and continuous adding were designed to study the variations of contaminants, respectively. The results of experiment show that when the ρ(C)/ ρ(P) ratio is lower than 34, phosphorus and nitrate are accumulated in A ²O, and the removal efficiency is worse; when the ρ(C)/ ρ(P) ratio is 45-59, the P removal efficiency maintains about 90%, and the effluent P concentration is lower than 0.5 mg/L; while the ρ(C)/ ρ(P) ratio is higher than 63, the P removal efficiency decreases as the ρ(C)/ ρ(P) ratio increases. In contrast, when the ρ(C)/ ρ(P) ratio is higher than 39, regardless of the ρ(C)/ ρ(P) ratio, excellent COD (90%) and TN (76%) removal efficiency are maintained throughout the experiments, and when the ρ(C)/ ρ(P) ratio are 57, the removal efficiency of the system are optimal. When the COD concentration are the same, the way of continuous adding not only can enhance availability of carbon source, but also increase anaerobic phosphorus release amount and improve denitrifying phosphorus and nitrate removal rate.