Abstract: Denitrifying Phosphorus Removal (DPR) was considered as one of the most promising biological treatment technologies, due to some superiorities of saving 50% carbon source, 30% energy requirement, and reducing 50% sludge production, regarding to N and P removal depend on nitrite and nitrate instead of oxygen. As a mixed cultivation process, limited carbon sources induced the competition of functional groups between Phosphorus Accumulation Organism (PAOS) and Glycogen Accumulation Organism (GAOs), as well as Ordinary Heterotrophic Organisms (OHOs). In this study, a lab scale Anaerobic/Anoxic/aerobic Sequencing Batch Reactor (An/A/O-SBR) was established to achieve a DPR process, with the sodium acetate (120 mg/L as COD) as electron donor, and NO3-/NO2- as electron acceptor (90 mmol/L). An investigation was made for the characteristics of nutrient removal, N2O release, as well as the contribution and competitive relationships between phosphorus and glycogen accumulating organisms (PAOs and GAOs) in the process after long term of acclimatization. During the anaerobic stage, the carbon source in raw wastewater was efficiently absorbed by PAOs (36%-62.3%) and GAOs (32.2%-55.7%), according to the sort of electron acceptor to enhance intracellular carbon storage. With NO3- as electron acceptor, the NO3- and PO43- removal efficiency was more than 95%, with 76.2% of nitrogen removal conducted by PAOs, and the rest by GAOs. In the anaerobic stage, the consumption of COD was stored in the form of PHA, while Gly was decomposed to provide energy for P release. The average P Release Amount (PRA) was 0.85 mmol/L with the PRA/ΔPHA of 0.29 mmol/mmol, close to the value of stoichiometry of typical DPAOs (0.24 mmol/mmol). During the anoxic stage, the average P Uptake Aamount (PUA) reached 28.9 mg/L. With NO2- as electron acceptor only, the N and P removal efficiency decreased to 69.9% and 50.5%, respectively. GAOs had a great advantage over PAOs at the presence of 30 mg/L nitrite, and it contributed to 76.2% of carbon absorption in an anaerobic stage and 49% of nitrogen removal in an anoxic stage. The PRA in anaerobic stage and PUA in anoxic stage decreased to 0.42 and 0.52mmol/L, respectively, with the PRA/ΔPHA decreased to 0.17 mmol/mmol and ΔGly/ΔPHA increased from 0.63 to 0.817 mmol/mmol. GAOs had a great tolerance to nitrite than PAOs, which alleviated the nitrite inhibition on PAOs at high nitrite concentration, thereby to ensure the nutrient removal in An/A/O-SBR.