A　system　consisting　of　a　two-stage　UASB　and　anoxic-oxic　reactor　was　used　to　study　the　influence　of　FA　on　short-cut　nitrification　of　the　actual　municipal　landfill　leachate　with　high　ammonia　concentration.　In　the　UASB1,　denitrification　and　methanogenesis　took　place　simultaneously.　The　effluent　COD　of　UASB1　was　further　removed　in　the　UASB2.　Then　the　denitrification　of　nitrite　and　nitrate　in　the　returned　sludge　by　using　the　residual　COD　and　nitrification　was　finished　in　the　A/O　reactor.　The　experiment　experienced　three　stages　during　79　d.　The　stable　short-cut　nitrification　was　achieved　in　the　first　stage　(40　d).　The　short-cut　nitrification　was　damaged　in　the　second　stage　(19　d),　and　the　short-cut　nitrification　was　recovered　in　the　last　stage　(20　d).　The　results　of　79　d　showed　that　when　the　FA　concentration　was　about　40-70　mg　x　L(-1),　the　stable　short-cut　nitrification　could　be　achieved.　For　example,　the　nitrite　accumulation　was　97%　in　the　system　during　the　first　stage,　and　the　ammonia　removal　efficiency　was　99%.　But　when　the　FA　concentration　was　about　160　mg　x　L(-1),　the　nitrification　would　be　inhibited.　In　the　third　stage,　raw　leachate　was　diluted　by　tap　water　in　order　to　decrease　the　FA　concentration.　And　then　the　short-cut　nitrification　was　recovered　soon.　In　a　word,　the　FA　concentration　is　an　important　factor　to　achieve　the　short-cut　nitrification　of　the　municipal　landfill　leachate.