The　partial　nitrification-anammox　(PNA)　process　under　intermittent　aeration　is　feasible　to　treat　low-strength　ammonium　wastewater,　but　the　effect　of　chemical　oxygen　demand　(COD)　on　mainstream　anammox　processes　is　not　fully　understood.　In　this　study,　PNA　process　was　established　for　sewage　treatment　(average　ammonium　=　59.3　mg-N/L)　in　a　sequencing　batch　reactor　(SBR)　with　intermittent　aeration　mode.　Influent　organic　carbon　to　nitrogen　(C/N)　ratios　were　gradually　increased　(1.1,　1.5,　2.0　and　2.5).　With　increasing　C/N　ratios,　the　total　nitrogen　(TN)　removal　efficiency　increased　steadily　from　30.8%　to　77.3%.　When　the　C/N　ratio　increased　from　1.1　to　2.0,　the　improvement　of　nitrogen　removal　was　attributed　to　the　increase　of　anammox　bacteria,　which　exponentially　increased　at　the　C/N　ratios　from　1.1　to　1.5.　Additionally,　nitrate　reduction　using　internal　carbon　was　likely　to　combine　with　anammox　reaction　under　intermittent　aeration　operation,　which　might　further　improve　the　nitrogen　removal.　Lastly,　settleability　and　particle　size　of　activated　sludge　were　also　improved　with　the　elevated　C/N　ratios,　which　favored　the　enrichment　of　anammox　bacteria　and　facilitated　the　combination　of　partial　denitrification　and　anammox.　When　the　C/N　ratio　was　2.5,　TN　removal　efficiency　still　increased　while　the　abundance　and　activity　of　anammox　bacteria　remained　stable,　indicating　that　influent　organic　carbon　promoted　denitrifying　bacteria　and　inhibited　anammox　bacterial　growth　rate.　Overall,　this　study　demonstrates　that　influent　COD　has　comprehensive　effects　on　PNA　systems　and　that　the　influent　C/N　ratios　are　suggested　to　adjust　within　optimal　range　to　achieve　long-term　stability.