The　treatment　of　landfill　leachate　obtained　from　municipal　solid　waste　(MSW)　by　using　a　lab-scale　sequencing　batch　reactor　(SBR)　was　studied.　The　aim　of　achieving　and　stabilizing　partial　nitrification　and　denitrification　and　the　characteristics　of　advanced　nitrogen　removal　were　investigated.　The　experimental　results　showed　that　for　95　days　running,　stable　partial　nitrification　with　nitrite　accumulation　rate　above　92.5%　was　achieved　and　maintained　successfully.　The　stable　biological　nitrogen　removal　via　partial　nitrification　and　denitrification　was　realized　and　the　average　removal　efficiency　of　NH4+-N　and　TN　were　above　97.2%　and　91.7%,　respectively.　The　DO,　ORP　and　pH　could　be　used　as　the　process　control　parameters　for　SBR　reactor,　because　the　characteristic　points　on　the　profiles　indicated　exactly　the　nitrification　and　denitrification　end　point.　The　nitrite　oxidizing　bacteria　(NOB)　was　more　sensitive　than　ammonia　oxidizing　bacteria　(AOB)　to　the　free　ammonia　(FA)　and　free　nitrite　acid　(FNA),　so　the　activity　of　NOB　was　inhibited　by　the　synergetic　effect　of　highly　concentrated　FA　and　FNA　in　the　SBR　nitrification.　Furthermore,　the　key　factor　of　achieving　and　stabilizing　partial　nitrification　and　denitrification　for　a　long　time　was　optimization　of　nitrifying　microbial　population　by　the　assistance　of　process　control,　which　was　proved　by　FISH　analysis.　©　All　Rights　Reserved.