A　gel　filler　with　diatomaceous　earth,　activated　carbon,　and　CaCO3　compounded　with　polyvinyl　alcohol　was　prepared　and　optimized.　Rapid　start-up　and　efficient　and　stable　operation　of　partial　nitrification　(PN)　was　achieved　by　immobilization　of　conventional　activated　sludge.　The　results　showed　that　the　proper　material　proportion　synergistically　improved　the　performance　and　oxygen　mass　transfer　rate　of　the　gel.　The　continuous　flow　reactor　was　operated　for　10d　to　successfully　start　PN,　and　the　maximum　ammonia　oxidation　rate　of　this　filler　was　58.30　mg　center　dot(L　center　dot　h)-　1　during　the　stable　operation,　and　the　nitrite　accumulation　rate　was　maintained　above　90　%.　However,　due　to　the　greater　mass　transfer　resistance　of　unoptimized　fillers,　more　dissolved　oxygen　waste　and　nitrogen　loss　were　caused,　resulting　in　delayed　expression　of　biological　activity.　Based　on　the　kinetic　characterization　of　ammonia-oxidizing　bacteria　(AOB)　within　the　filler　and　high-throughput　sequencing,　it　was　demonstrated　that　the　rapid　start-up　and　efficient　and　stable　operation　of　the　PN　system　was　due　to　the　highly　oxygenophilic　and　community-dominant　position　of　AOB　within　this　filler.　This　study　provides　new　options　and　insights　at　the　level　of　immobilization　technology　for　the　realization　and　efficient　and　stable　operation　of　PN.