In order to investigate the performance of biological nutrients removal and denitrifying phosphorus removal in the A2O process when treating low C/N ratio domestic wastewater，a reactor，with a working volume of 52.5 L，was used in this study.The volume ratio of anaerobic/anoxic/aerobic zone was 1/1/2 and the major operating parameters were：HRT 8 h，sludge recycle ratio（r）70%，aerobic（nitrate）recycle ratio（R）300%.The results showed that 85.4% of TN and 93.3% of SOP could be removed when the C/N ratio was 7.89.There was denitrifying phosphorus removal in the system.Moreover，up to 25.3% of the SOP could be removed in the anoxic zone by this way.The TN removal efficiency was reduced to 62.2% when decreasing the C/N ratio to 4.20 with the same operating parameters.However，the SOP removal efficiency was kept over 96.0%.The TN removal efficiency was 70.7% and up to 55.2% of SOP was removed in the anoxic zone when changing the volume ratio of anoxic/aerobic to 5/8.With the same anoxic/aerobic ratio，when changing the aerobic（nitrate）recycle ratio to 250%，the maximal denitrifying phosphorus removal could be achieved，removing 77.3% of the TN from the system.Enhanced denitrifying phosphorus removal in the A2O process is an effective way to counteract the disadvantages of carbon shortage for biological nutrients removal.