In　photocatalysis,　reducing　the　exciton　binding　energy　and　boosting　the　conversion　of　excitons　into　free　charge　carriers　are　vital　to　enhance　photocatalytic　activity.　This　work　presents　a　facile　strategy　of　engineering　Pt　single　atoms　on　a　2D　hydrazone-based　covalent　organic　framework　(TCOF)　to　promote　H2　production　coupled　with　selective　oxidation　of　benzylamine.　The　optimised　TCOF-Pt　SA　photocatalyst　with　3　wt%　Pt　single　atom　exhibited　superior　performance　to　TCOF　and　TCOF-supported　Pt　nanoparticle　catalysts.　The　production　rates　of　H2　and　N-benzylidenebenzylamine　over　TCOF-Pt　SA3　are　12.6　and　10.9　times　higher　than　those　over　TCOF,　respectively.　Empirical　characterisation　and　theoretical　simulation　showed　that　the　atomically　dispersed　Pt　is　stabilised　on　the　TCOF　support　through　the　coordinated　N1-Pt-C2　sites,　thereby　induing　the　local　polarization　and　improving　the　dielectric　constant　to　reach　the　low　exciton　binding　energy.　These　phenomena　led　to　the　promotion　of　exciton　dissociation　into　electrons　and　holes　and　the　acceleration　of　the　separation　and　transport　of　photoexcited　charge　carriers　from　bulk　to　the　surface.　This　work　provides　new　insights　into　the　regulation　of　exciton　effect　for　the　design　of　advanced　polymer　photocatalysts.　©　2023　Wiley-VCH　GmbH.