Sunlight　-induced　photocatalytic　carbon　dioxide　(CO2)　reduction　to　energy　-rich　chemicals　by　metal　-free　polymeric　carbon　nitride　(CN)　semiconductor　is　a　promising　tactic　for　sustained　solar　fuel　production.　However,　the　reaction　efficiency　of　CO2　photoreduction　is　restrained　seriously　by　the　rapid　recombination　of　photogenerated　carriers　on　CN　polymer.　Herein,　we　incorporate　2-aminopyridine　molecule　with　strong　electron　-withdrawing　group　into　the　skeleton　edge　of　CN　layers　through　a　facile　one　-pot　thermal　polymerization　strategy　using　urea　as　the　precursor,　which　renders　a　modified　carbon　nitride　(ACN)　with　extended　optical　harvesting,　abundant　nitrogen　defects　and　ultrathin　nanosheet　structure.　Consequently,　the　ACN　photocatalyst　with　desirable　structural　features　attains　enhanced　separation　and　migration　of　photoexcited　charge　carriers.　Under　visible　light　irradiation　with　Co(bpy)32+　as　a　cocatalyst,　the　optimized　ACN　sample　manifests　a　high　CO2　deoxygnative　reduction　activity　and　high　stability,　providing　a　CO　yielding　rate　of　17　mu　mol　h-1,　which　is　significantly　higher　than　that　of　pristine　CN.　The　key　intermediates　engaged　in　CO2　photoreduction　reaction　are　determined　by　the　in　situ　diffuse　reflectance　infrared　Fourier　transform　spectroscopy,　which　sponsors　the　construction　of　the　possible　photocatalytic　CO2　reduction　mechanism　on　ACN　nanosheets.