A　combined　process　of　a　two-stage　up-flow　anaerobic　sludge　blanket　(UASB),　an　anoxic/aerobic　(A/O)　reactor　and　a　sequencing　batch　reactor　(SBR)　was　used　to　treat　mature　landfill　leachate,　and　the　influencing　factors　on　short-cut　nitrification　in　A/O　reactor　were　also　researched.　The　operational　mode　of　the　process　was　as　follows:　Denitrification　took　place　in　the　first　stage　UASB　(UASB1).　The　residual　nitrite　and　nitrate　of　UASB1　by　using　the　residual　chemical　oxygen　demand　(COD)　was　further　removed　in　the　second　stage　UASB　(UASB2).　The　ammonia　nitrogen　was　removed　by　short-cut　nitrification　in　the　aerobic　zone　of　A/O　reactor.　The　nitrite　and　nitrate　produced　from　the　nitrification　were　removed　in　SBR.　The　experiment　results　show　that　the　COD　and　ammonia　nitrogen　mass　concentrations　of　raw　leachate　are　about　3.0　g/L　and　2.0　g/L,　respectively.　The　influent　leachate　is　mixed　by　raw　leachate　as　well　as　domestic　wastewater　in　a　ratio　of　1.　The　external　carbon　source　(sodium　acetate　anhydrous)　is　added　in　order　to　enhance　the　ρ(C)/ρ(N)　ratio　from　1.7　to　3.0.　Through　the　cooperative　inhibition　of　the　free　ammonia　(FA)　and　free　nitrite　acid　(FNA),　the　short-cut　nitrification　is　achieved　stably　in　the　A/O　reactor　with　more　than　70%　of　the　nitrite　accumulation　ratio.　The　nitrite　and　nitrate　produced　from　the　nitrification　could　be　removed　completely　in　SBR.　The　ammonia　mass　concentration　of　final　effluent　is　less　than　2　mg/L,　and　its　removal　efficiency　is　99%.　The　total　nitrogen　mass　concentration　of　final　effluent　is　about　26　mg/L,　and　its　removal　efficiency　is　about　98%.