The　efficient　removal　of　highly　toxic　polyhalogenated　biphenyls　is　rather　challenging,　mainly　due　to　the　difficulties　in　splitting　C-X　(X　=　Cl　or　Br)　bond　with　high　bond　energy,　as　well　as　the　transfer　of　active　hydrogen　species　during　the　reduction　dehalogenation　process.　In　this　work,　sub-nanometer　Pd-Pt　alloy　clusters　(ca.　1　nm)　supported　on　defect-containing　TiO2(B)　nanosheets　(PdPt/TB),　on　absorption　of　visible　light　illumination　(lambda　＞　400　nm),　were　prepared　and　served　as　an　efficient　photocatalysts　for　dehalogenation　of　polyhalogenated　biphenyls　with　H2O　as　the　hydrogen　source.　An　optimal　sample　(Pd0.7Pt0.3/TB)　shows　the　highest　photocatalytic　dehalogenation　efficiency　for　3,3　＇,4,4　＇-trtrachlorobiphenyl　(PCB77)　within　30　mins,　which　is　12.5,　3.5　and　3　times　higher　than　that　of　Pt-1/TB,　Pd-1/TB,　and　Pd-0.7　+　Pt-0.3/TB　samples,　respectively.　Besides,　4,4　＇-dibromobiphenyl　(PBB15)　was　also　completely　removed　within　10　mins　by　using　Pd0.7Pt0.3/TB　photocatalyst,　demonstrating　its　potential　applications.　Experiments　and　d-band　theory　calculations　revealed　that　the　introduction　of　Pt　can　regulate　the　d-band　center　of　Pd　to　strength　the　interaction　between　active　hydrogen　with　alloy　and　promote　the　transfer　of　hydrogen　species.　Meanwhile,　Pd-Pt　alloy　is　conducive　to　activate　the　C-X　bond　of　polyhalogenated　biphenyls.　Finally,　a　mechanism　based　on　Pd-Pt　alloy　clusters　synergistic　interaction　is　proposed　at　the　molecular　level.　This　work　demonstrates　the　successful　synthesis　of　sub-nanometer　Pd-Pt　alloy　nanoclusters　and　elucidates　the　effect　of　interaction　among　Pd,　Pt　and　supports,　providing　an　efficient　method　for　the　removal　of　polyhalogenated　compounds　by　photocatalytic　technology.