Highly　crystalline　carbon　nitride　polymers　have　shown　great　opportunities　in　overall　water　photosplitting;　however,　their　mission　in　light-driven　CO2　conversion　remains　to　be　explored.　In　this　work,　crystalline　carbon　nitride　(CCN)　nanosheets　of　poly　triazine　imide　(PTI)　embedded　with　melon　domains　are　fabricated　by　KCl/LiCl-mediated　polycondensation　of　dicyandiamide,　the　surface　of　which　is　subsequently　deposited　with　ultrafine　WO3　nanoparticles　to　construct　the　CCN/WO3　heterostructure　with　a　S-scheme　interface.　Systematic　characterizations　have　been　conducted　to　reveal　the　compositions　and　structures　of　the　S-scheme　CCN/WO3　hybrid,　featuring　strengthened　optical　capture,　enhanced　CO2　adsorption　and　activation,　attractive　textural　properties,　as　well　as　spatial　separation　and　directed　movement　of　light-triggered　charge　carriers.　Under　mild　conditions,　the　CCN/WO3　catalyst　with　optimized　composition　displays　a　high　photocatalytic　activity　for　reducing　CO2　to　CO　in　a　rate　of　23.0　mu　mol/hr　(　i.e.,　2300　mu　mol/(hr　center　dot　g)),　which　is　about　7-fold　that　of　pristine　CCN,　along　with　a　high　CO　selectivity　of　90.6%　against　H2　formation.　Moreover,　it　also　manifests　high　stability　and　fine　reusability　for　the　CO2　conversion　reaction.　The　CO2　adsorption　and　conversion　processes　on　the　catalyst　are　monitored　by　in-situ　diffuse　reflectance　infrared　Fourier　transform　spectroscopy　(DRIFTS),　identifying　the　crucial　intermediates　of　CO2　*-,　COOH*　and　CO*,　which　integrated　with　the　results　of　performance　evaluation　proposes　the　possible　CO2　reduction　mechanism.　(c)　2023　The　Research　Center　for　Eco-Environmental　Sciences,　Chinese　Academy　of　Sciences.　Published　by　Elsevier　B.V.