The　chemical　oxygen　demand　(COD)　to　total　inorganic　nitrogen　ratios　(C/N)　fluctuations　under　mainstream　conditions　has　a　crucial　influence　on　the　performance　of　partial　nitrification-anammox　(PNA)　systems.　In　this　study,　a　PNA　sequencing　batch　reactor　was　applied　for　real　municipal　wastewater　treatment　with　a　continuous　decrease　in　C/N　(4.3　to　1.4).　The　results　showed　that　with　the　decrease　of　C/N,　the　nitrite　accumulation　ratio　(NAR)　decreased　from　94.1%　to　60.7%,　and　nitrogen　removal　by　endogenous　denitrification　was　attenuated.　However,　the　nitrogen　removal　efficiency　(NRE)　significantly　increased　from　43.8%　to　91.5%,　which　was　attributed　to　the　enhanced　performance　of　PNA　under　aerobic　conditions　and　additional　nitrite　provided　by　endogenous　partial　denitrification　(EPD)　for　anammox　under　anoxic　conditions.　Glycogen　accumulating　or-ganisms　(GAOs)　that　dominated　the　EPD　process　increased　remarkably　from　0.42%　to　2.78%　exhibiting　a　competitive　advantage　over　phosphorus　accumulating　organisms　(PAOs)　at　low　organic　loads.　Co-existence　of　highly　enriched　anammox　bacteria　(0.91%)　and　GAOs　(2.78%)　ensured　the　enhanced　nitrogen　removal　during　the　aerobic　and　anoxic　phases.　This　study　provides　in-depth　perspectives　on　the　PNA　combing　with　EPD　under　varied　C/N　and　broadening　the　flexibility　of　PNA　applications.