In　low-ammonia　sewage　anammox　process,　cultivation　and　enrichment　of　anammox　bacteria　(AnAOB)　is　a　challenge　especially　from　traditional　activated　sludge.　To　this　end,　a　novel　strategy　solely　using　activated　sludge　as　inoculum　and　biocarrier　in　a　dynamic　fixed-bed　reactor　was　proposed　in　this　study.　During　115-day　operation,　excellent　performance　was　achieved　with　influent　total　inorganic　nitrogen　(TIN)　and　effluent　TIN　of　55.3　mg.L-1　and　4.1　mg.L-1,　respectively.　Rapid　enrichment　of　AnAOB　(doubling　time:　8.5　days)　was　demonstrated　by　augmented　specific　anammox　activity　(trace　value　to　1.85　mg　N.g　VSS-1.h(-1))　and　increased　hzsB　gene　number　(10(6)　to　10(9)　copies.g(-1)　dry　sludge),　with　predominance　of　Candidatus_Brocadia.　Large-flocs　aggregate　was　the　primary　habitat　for　AnAOB　with　highest　abundance　and　capacity.　The　distinctive　sludge　properties,　symbiotic　microbial　interactions　and　dynamic　operation　scheme　facilitated　AnAOB　growth　and　retention.　This　study　provides　a　simple,　economic　and　workable　approach　for　the　start-up　of　mainstream　anammox　process.