The　stable　nitrite　(NO2--N)　generation　and　rapid　startup　of　anammox-based　process　are　the　main　bottlenecks　hindering　its　application　in　mainstream　municipal　wastewater　treatment.　In　this　study,　a　Partial-Denitrification　(PD)　system　re-ducing　nitrate　(NO3--N)　to　NO2--N　was　rapidly　developed　within　40　days,　using　the　nitrification/denitrification　sludge　from　wastewater　treatment　plant.　The　NO3--N　to　NO2--N　transformation　ratios　achieved　80.6　%.　Significantly,　a　fast　self-enrichment　of　anammox　bacteria　in　this　system　was　subsequently　obtained,　resulting　in　the　successful　transforma-tion　to　an　efficient　PD/Anammox　(PD/A)　process　after　79-day　operation.　The　total　nitrogen　removal　efficiency　in-creased　from　12.4　%　to　90.0　%　with　influent　ammonia　and　nitrate　of　45.9　mg　N/L　and　62.2　mg　N/L,　corresponding　to　the　anammox　activity　significantly　increasing　to　6.0　mgNH(4)(+)-N/g　VSS/h　without　seeding　anammox　sludge.　Abun-dance　of　anammox　increased　from　6.7　x　10(8)　to　2.0　x　10(11)　copies/g　dry　sludge.　High-throughput　sequencing　results　showed　that　Candidatus　Brocadia　was　the　only　known　anammox　genus　and　accounted　for　1.08　%　during　the　PD/A　stage.　Functional　bacteria　for　PD,　assumed　to　be　the　Thauera,　was　enriched　from　1.99　%　to　60.06　%　but　decreased　to　32.49　%　during　the　improvement　of　anammox　activity.　It　demonstrated　that　the　PD　system　with　stable　NO2--N　accumulation　enabled　a　rapid　self-enrichment　of　anammox　bacteria　and　sufficient　nitrogen　removal　with　ordinary　nitrification/denitrification　sludge.　This　provides　new　insights　into　the　scaling　application　of　anammox　by　integrating　PD　with　shortened　startup　periods　and　improved　TN　removal　efficiency.