This　study　applied　combined　spectroscopy　techniques　to　assess　rDOM　compositional　characteristic　and　investigated　its　transformation　mechanisms　during　the　treatment　of　mature　landfill　leachate　by　ANAMMOX　process.　A　novel　rDOM　metabolism　mechanism　was　proposed　in　this　study　for　the　first　time.　A　stable,　high　nitrogen　removal　rate　of　5.95　kg　N/m(3)/day　and　a　rDOM　conversion　efficiency　of　51%　were　achieved　in　ANAMMOX　reactor　(AR).　In　additionally,　the　initial　rDOM　removal　was　closely　related　to　sludge　adsorption,　with　the　adsorption　force　mainly　originating　from　electrostatic　interaction　and　hydrophobicity.　As　the　operating　time　increased,　the　removal　mechanism　of　rDOM　in　the　AR　changed　from　adsorption　to　adsorption-biodegradation　and　finally　stabilized.　Furthermore,　Anaerolineaceae,　associated　with　the　hydrophobic　reaction,　were　the　primary　degraders　for　the　rDOM　and　Candidatus　Kuenenia　dominated　the　nitrogen　consumption.　rDOM　removal　efficiency　was　suggested　to　be　increased　by　a　moderate　enhancement　of　Anaerolineaceae　content　in　the　AR.