A　partial-denitrification　coupling　with　anaerobic　ammonium　oxidation　(anammox)　process　(PD/A)　in　a　continuous-flow　anoxic/oxic　(A/O)　biofilm　reactor　was　developed　to　treat　carbon-limited　domestic　wastewater　(ammonia　(NH4+-N)　of　55　mg/L　and　chemical　oxygen　demand　(COD)　of　148　mg/L　in　average)　for　about　200　days　operation.　Satisfactory　NH4+-N　oxidation　efficiency　above　95%　was　achieved　with　rapid　biofilm　formation　in　the　aerobic　zone.　Notably,　nitrite　(NO2--N)　accumulation　was　observed　in　the　anoxic　zone,　mainly　due　to　the　insufficient　electron　donor　for　complete　nitrate　(NO3--N)　reduction.　The　nitrate-to-nitrite　transformation　ratio　(NTR)　achieved　was　as　high　as　64.4%.　After　the　inoculation　of　anammox-enriched　sludge　to　anoxic　zones,　total　nitrogen　(TN)　removal　was　significantly　improved　from　37.3%　to　78.0%.　Anammox　bacteria　were　effectively　retained　in　anoxic　biofilm　utilizing　NO2--N　produced　via　the　PD　approach　and　NH4+-N　in　domestic　wastewater,　with　the　relative　abundance　of　5.83%　for　stable　operation.　Anammox　pathway　contributed　to　TN　removal　by　a　high　level　of　38%.　Overall,　this　study　provided　a　promising　method　for　mainstream　nitrogen　removal　with　low　energy　consumption　and　organic　carbon　demand.