Abstract: The selection and dominance of denitrifying phosphorus removing bacteria(DPB),which was capable of utilizing nitrate as electron acceptor,was investigated in a laboratory-scale sequencing batch moving-bed biofilm reactor(MBBR).The experimental results demonstrated that the proportion of DPB increased approximately from 11.77% to 66.07% of total phosphate accumulating organisms(PAOs) after three stages selection and dominance.In the end of the third cultivating period,average removal efficiencies of COD and TP were 68.78% and 69.02%,respectively,and a large quantity of nitrate,23.91 mg/L,was removed in anoxic phase.It was found that a great deal of PHB about PAOs emerged in anaerobic phase,whereas a mass of Poly-p about PAOs arose in anoxic phase by biofilm dyeing method,so they could be taken as evidences to judge the process and efficiency of biological phosphorus removal.