Although　thermal　hydrolysis　pretreatment　enhances　disposal　efficiency　of　sludge,　it　inevitably　leads　to　melanoidins　formation,　which　will　negatively　impact　the　subsequent　wastewater　treatment　processes.　However,　their　effect　on　the　dewaterability　of　thermal　hydrolyzed　sludge　(THS)　remains　poorly　understood.　This　study　aimed　to　uncover　the　underlying　mechanisms　of　how　melanoidins　affecting　dewaterability　of　THS.　Using　resin-adsorption　method　to　reduce　melanoidins　content　by　50%　led　to　21%　and　6%　decreases　in　capillary　suction　time　and　specific　resistance　to　filtration,　respectively,　and　a　14%　increase　in　sludge　cake　solid　content.　Conversely,　accumulating　melanoidins　to　200%　worsened　THS　dewaterability,　altering　surface　morphology　and　reducing　floc　stability,　which　increased　the　content　of　bound　water　by　9%.　Additionally,　a　higher　melanoidins　level　increased　the　hydrophilic　components　in　extracellular　polymeric　substances　while　reducing　hydrophobic　sites　and　structures.　These　findings　indicate　that　melanoidins　impair　THS　dewaterability　by　altering　flocs　spatial　properties　and　increasing　hydrophilic　structures　and　components.