MXene　quantum　dots　(QDs)　possess　the　electron-withdrawing　capability　of　MXene　nanosheets　(NSs)　with　more　abundant　active　sites,　rendering　it　an　emerging　charge　mediator　for　photocatalysis.　Nevertheless,　few　MXene　QD-based　photocatalytic　systems　have　been　explored,　and　the　contribution　of　MXene　QDs　for　the　modulation　of　charge　transfer　remains　elusive.　Herein,　we　show　the　construction　of　cascade　charge　flow　over　transition　metal　chalcogenides　(TMCs),　which　are　coated　via　a　polyelectrolyte　layer　of　poly(dialyldimethylammonium　chloride)　(PDDA),　followed　by　MXene　QD　deposition.　It　was　unleashed　that　the　intermediate　PDDA　layer　serves　as　a　charge　relay　medium　to　boost　the　electron　transfer　from　TMC　NSs　to　MXene　QDs,　boosting　the　charge　transfer　kinetics,　promoting　the　interfacial　charge　separation,　and　endowing　the　TMCs@PDDA-M　QD　heterostructures　with　considerably　enhanced　visible-light-driven　photoactivities　for　reduction　of　aromatic　nitro　compounds.