In　enhanced　biological　phosphorus　removal　(EBPR)　from　wastewater,　the　metabolism　pathway　of　polyphosphate　accumulating　organisms　(PAOs)　converted　from　polyphosphate　accumulating　metabolism　(PAM)　to　glycogen　accumulating　metabolism　(GAM)　under　a　high　ratio　of　carbon　to　phosphorus　(C/P).　This　study　investigated　the　competition　mechanism　between　PAOs　and　glycogen　accumulating　organisms　(GAOs)　under　GAM　pathway.　Low　acetic　acid　(HAC)　concentration　made　the　GAM　of　PAOs　outcompete　GAOs　in　high　C/P　ratio　(100:1),　and　the　effect　of　influent　acetate　concentration　on　GAOs　was　stronger　than　PAOs.　＂Candidates　Accumulibacter＂　clades　IIC　and　IID　were　the　main　dominant　PAOs,　and　Thiothrix　caldifontis　(potential　PAOs)　was　discovered　and　significantly　increased　from　0.53%　to　5.75%.　Flow　cytometry　results　indicated　that　PAOs　had　higher　specific　surface　area　and　lower　nucleic　acid　content　than　GAOs,　and　high　C/P　promoted　GAM　rather　than　GAOs　growth,　which　maybe　important　reasons　causing　PAOs　dominant　growth.　PAOs　dominance　under　GAM　ensured　stable　performance　of　EBPR　when　C/P　ratio　in　real　wastewater　increased.