A　combined　system　consisting　of　an　up-flow　anaerobic　sludge　blanket　(UASB)　and　anoxic/oxic　bioreactor　was　adopted　for　treating　mature　municipal　landfill　leachate.　The　transition　behavior　of　nitrogen　and　organic　matter　and　the　comprehensive　effects　in　the　combined　system　were　systematically　analyzed　at　different　organic　loading　rates　(OLR)　(3.78-20.25　kg/(m3·d)).　The　results　show　that　the　total　COD　removal　rate　is　above　90%　due　to　the　dynamic　buffer　ability　of　anaerobic　and　aerobic　system;　ammonia　nitrogen　(NH4+-N)　removal　rate　decreases　due　to　the　lack　of　alkalinity　with　low　OLR　and　the　competition　of　heterotrophic　bacteria　with　high　OLR;　total　nitrogen　removal　rate　ascends　with　the　increase　of　OLR,　and　when　OLR　is　too　low,　total　nitrogen　removal　rate　decreases　obviously　with　the　double　restriction　of　carbon　source　for　denitrifying　and　low　efficiency　of　NH4+-N　degradation;　in　the　anaerobic　simultaneous　denitrification　and　methanogenesis　reactor,　volatile　fatty　acid　(VFA)/alkalinity　value　is　lower　than　0.3　and　denitrifying　bacteria　and　methane-producing　bacteria　are　maintained　at　dynamic　balance　in　the　OLR　range　of　6.15-15.58　kg/(m3·d);　there　are　different　features　while　using　DO　and　pH　curve　as　electrochemical　parameters　of　real-time　control,　and　it　is　necessary　to　combine　these　two　methods　according　to　variation　rule;　and　the　nitrite　accumulation　rate　in　A/O　presents　a　modest　increase　with　the　increase　of　OLR.