Carbon　quantum　dots　(CQDs)　are　emerging　as　the　new-generation　light　absorber　for　solar　energy　conversion.　However,　the　low　photosensitization　efficiency　of　CQDs　is　one　of　the　current　bottlenecks　impeding　their　large-scale　practical　applications　in　photocatalysis.　Therefore,　developing　a　facile　approach　for　the　engineering　and　functionalization　of　CQDs-based　composites　to　improve　the　photosensitization　efficiency　of　CQDs　is　highly　desirable.　On　account　of　the　abundant　functional　groups,　especially　oxygen-containing　functional　groups　such　as　carbonyl,　carboxyl,　and　hydroxyl　present　on　their　surface,　CQDs　can　be　readily　combined　with　various　organic　molecules　or　polymers　as　a　surface　passivation　component　to　reduce　the　nonradioactive　surface　recombination　of　photo-generated　charge　carriers,　thus　enabling　the　CQDs　to　exhibit　strong　photoluminescence　in　the　visible　and　near-infrared　spectral　regions.　Consequently,　polymer　passivation　has　been　demonstrated　as　an　ideal　strategy　to　make　it　accessible　for　improving　the　sensitization　efficiency　of　CQDs　in　photocatalytic　applications.　Branched　polyethylenimine　(BPEI)　is　one　of　polymers　that　contains　a　high　density　of　amine　groups　and　exhibits　high　electron　mobility,　which　can　be　used　as　an　electron　injection　material　at　the　interface　of　nanomaterials.　Besides,　the　BPEI　polymer　with　amino　groups　exhibiting　positive　charge　has　been　utilized　for　designing　heterogeneous　catalysts　by　an　electrostatic　self-assembly　strategy.　Therefore,　BPEI　is　expected　to　modify　the　surface　of　inorganic　oxides　semiconductor　to　enhance　the　photosensitization　efficiency　of　CQDs　under　visible　light.　However,　to　date,　the　study　in　this　regard　has　been　still　unavailable.　In　this　work,　we　developed　a　facile　approach　to　engineer　well-distributed　CQDs　via　electrostatic　interaction　on　BPEI　passivated　TiO2　composites　(BTC)　as　photocatalysts.　The　BTC　composites　with　an　optimal　loading　of　5%　(w,　mass　fraction)　CQDs　outperformed　the　TiO2/CQDs　(TC)　composite　and　referential　BPEI/SiO2/CQDs　(BSC)　composites　for　the　photoreduction　of　4-nitroaniline　under　visible　light　irradiation.　The　structure　of　the　fabricated　BTC　composites　was　systematically　investigated　by　the　combined　use　of　structural　and　spectral　characterizations,　demonstrating　that　the　photosensitizer　CQDs　contacted　well　with　the　BPEI　modified　TiO2　nanoparticles.　The　comparison　characterizations　revealed　that　BPEI　facilitated　the　dissociation　and　transfer　of　excitons　as　an　electron　transfer　channel.　The　as-prepared　BTC　composites　benefited　from　the　favorable　interfacial　contact　and　effective　transfer　of　photo-generated　charge　carriers,　and　thus　manifested　superior　photocatalytic　activity　to　the　TC　composite.　It　is　expected　that　this　strategy　would　be　extended　to　other　wide　band　gap　semiconductor　photocatalyst　systems　and　open　up　new　possibilities　in　designing　efficient　CQDs-based　semiconductor　artificial　light　harvesting　systems　by　interfacial　optimization.