Long-term　high　efficiency　and　stable　partial　nitrification　(PN)　performance　was　achieved　using　gel-immobilized　partial　nitrifying　bacteria.　The　PN　characteristics　of　the　filler　under　high　and　low　ammonia　nitrogen　concentrations　and　low　temperature　were　comprehensively　studied　and　the　rapid　reactivation　was　achieved　after　reactor　breakdown　or　long　stagnation　period.　The　results　showed　that　the　maximum　ammonia　oxidation　rate　was　66.8　mg•(L•h)−1　and　the　nitrite　accumulation　rate　was　above　95　%　for　the　filler.　Efficient　and　stable　PN　performance　depends　on　the　high　abundance　of　ammonia-oxidizing　bacteria　(AOB)　inside　the　filler　and　dynamically　microbial　community.　In　addition,　the　oxygen-limited　zone　and　competition　between　the　microorganisms　inside　the　filler　effectively　inhibited　the　growth　of　nitrite　oxidizing　bacteria,　and　the　sludge　outside　the　filler　assisted　in　this　process,　which　supported　the　dominant　position　of　AOB　in　fillers.　This　study　provides　a　reliable　technology　for　the　practical　application　of　the　PN　nitrogen　removal　process.　©　2023　Elsevier　Ltd