Achieving　maximum　atom-utilization　efficiency　is　desirable　to　facilitate　the　charge　separation　and　CO2　activation　for　photocatalytic　CO2　reduction.　Herein,　we　report　a　well-defined　positioned　synthesis　of　Pt　single　atoms　in　ethylene　glycol　(EG)-modified　covalent　triazine　framework　(Pt-SA/CTF-1)　via　a　photo-deposition　method　for　efficient　photoreduction　CO2　to　CH4　under　visible　light　irradiation.　The　well-defined　coordination　structure　of　Pt-N(C)　sites　in　the　Pt-SA/CTF-1　catalyst　has　been　probed　by　HAADF-STEM　and　EXAFS.　Results　show　that　Pt　single　atoms　confined　into　CTF-1　not　only　improved　CO2　adsorption　and　activation　but　also　accelerated　the　separation　and　transfer　of　photogenerated　carriers　in　CTF-1.　Consequently,　Pt-SA/CTF-1　exhibited　superior　photoactivity　and　stability,　which　significantly　surpass　the　Pt　nanoparticles-based　CTF-1,　affording　CH4　as　the　main　reduction　product.　This　work　showcases　an　operable　avenue　to　develop　single-metal-atom　photocatalysts　and　a　mechanistic　insight　into　photoreduction　of　CO2　by　CTF-based　composite.