The　landfill　leachate　treatment　was　investigated　by　using　an　UASB-SBR　biological　system.　The　long-term　stability　of　nitrogen　removal　via　nitrite　at　normal　and　low　temperature　was　studied.　Furthermore,　the　achievement　mechanism　of　partial　nitrification　and　characteristic　of　nitrifying　bacteria　were　investigated　in　SBR.　598days　experimental　result　showed　that　the　removal　efficiencies　of　COD,　NH4+-N　and　TN　reached　92.0%,　99.2%　and　98.0%,　respectively.　The　advanced　nitrogen　removal　was　achieved　in　the　system.　Partial　nitrification　was　achieved　after　116days　operation　in　SBR,　and　nitrite　accumulation　ratio　(NAR)　reached　above　90%.　The　higher　NAR　was　maintained　for　171days　at　low　15°C　and　the　lowest　temperature　of　10.2°C　during　two　winters.　The　effect　of　free　ammonia　(FA)　inhibition　and　process　control　was　used　to　achieve　nitrite　pathway　in　the　SBR.　The　ammonia　oxidizing　bacteria　(AOB)　was　dominant　by　fluorescence　in　situ　hybridization　(FISH)　techniques　analysis,　and　the　spherical　Nitrosococcus　and　rod-shaped　Nitrosomonas　were　dominant　in　ammonia　oxidizing　bacteria　by　scanning　electron　microscope　(SEM)　techniques　analysis.