Enhanced denitrifying phosphorus removal in anaerobic-anoxic/oxic (A2O) process is an effective way to increase the removal efficiency of nitrogen and phosphorus when treating low C/N ratio domestic wastewater.In this study，a 52.5L pilot-scale reactor，based on plug-flow A2O configuration，was used to treat domestic wastewater.In addition，the microbial population variation was investigated by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE）.The results showed that the microbial community structure and dominant bacteria changed with the variation of wastewater quality and operating parameters.The dynamic change of microbial population was consistent with the variation of operation.Sequence results of DGGE bands showed that the dominant bacterial community in the system was Proteobacteria.Acinetobacter may be responsible for the traditional biological phosphorus removal in the system，but it disappeared gradually with the enhancement of denitrifying phosphorus removal.Uncultured Chlorobi bacterium increased with the enhancement of denitrifying phosphorus removal and it might be the major denitrifying phosphate accumulating organisms (DPAOs) in the system.