Mature　landfill　leachate　with　high　ammonia　concentration　was　treated　by　a　combined　system　consisting　of　a　up-flow　anaerobic　sludge　blanket　(UASB),　an　anoxic/aerobic　(A/O)　reactor　and　a　sequencing　batch　reactor　(SBR).　Denitrification　and　methanogenesis　were　carried　out　simultaneously　in　the　UASB　and　then　the　denitrification　of　nitrite　and　nitrate　in　the　returned　sludge　were　accomplished　in　the　A/O　reactor.　The　residual　ammonia　as　well　as　nitrite　and　nitrate　was　removed　in　SBR.　The　partial　biological　nitrogen　removal　was　achieved　stably　both　in　A/O　reactor　with　FA　control　and　in　SBR　with　process　control　strategy　with　94%　and　93%　nitrite　accumulation,　respectively,　and　microbial　analysis　data　showed　AOB　and　NOB,　respectively,　accounted　for　3.5%　and　0.2%　of　the　total　amount　of　bacteria　in　A/O　reactor　and　accounted　for　4%　and　0.4%　in　SBR.　when　the　total　nitrogen　(TN)　concentration　of　influent　leachate　was　about　2080　mg/L　and　the　ammonia　nitrogen　concentration　was　about　1970　mg/L,　Nitrification　and　nitrogen　removal　were　usually　both　higher　than　99%　and　the　TN　and　NH4+-N　of　final　effulent　were　about　12　mg/L　and　6　mg/L,　respectively.　The　key　factor　of　achieving　and　stabilizing　partial　nitrification　in　combined　system　was　the　optimization　of　nitrifying　communities　in　sludge　owing　to　long-term　application　of　FA　inhibition　and　process　control.