In　anaerobic/aerobic/anoxic　(A/O/A)　process,　endogenous　denitrification　(ED)　is　critically　important,　and　achieving　steady　endogenous　partial　denitrification　(EdPD)　is　crucial　to　carbon　saving　and　anammox　application.　In　this　study,　EdPD　was　rapidly　realized　from　conventional　activated　sludge　by　expelling　phosphorus　accumulating　organisms　(PAOs)　in　anaerobic/anoxic　(A/A)　mode　during　40　days,　with　nitrite　transformation　rate　(NTR)　surging　to　82.8　%　from　29.4　%.　Competibacter　was　the　prime　EdPD-fulfilling　bacterium,　soaring　to　28.9　%　from　0.5　%　in　phase　II.　Afterwards,　balance　of　high　NTR　and　phosphorus　removal　efficiency　(PRE)　were　attained　by　well　regulating　competition　and　cooperation　between　PAOs　and　glycogen　accumulating　organisms　(GAOs)　in　A/　O/A　mode,　when　the　Competibacter　(21.7　%)　and　Accumulibacter　(7.3　%,　mainly　Acc_IIC　and　Acc_IIF)　were　in　dominant　position　with　balance.　The　PRE　recovered　to　88.6　%　and　NTR　remained　67.7　%.　Great　balance　of　GAOs　and　PAOs　contributed　to　advanced　nitrogen　removal　by　anammox.