Covalent　triazine　frameworks　(CTFs)　are　emerging　as　promising　platform　for　photocatalysis,　yet　their　highly　symmetric　structure　leads　to　significant　charge　recombination.　Herein,　we　employed　a　facile　non-metallic　boron　(B)　modification　with　precisely　controlled　doping　site　to　introduce　asymmetric　local　electron　distribution　in　CTFs,　achieving　a　15-fold　activity　enhancement　for　CO2-to-CH4　conversion.　Calculations　including　frontier　orbitals,　dipole　moments　and　molecular　electrostatic　potentials　firmly　demonstrated　the　formation　of　localized　polarized　electron　regions　in　CTF-1　via　B　doping.　Noteworthily,　the　primary　coordination-activation　site　for　CO2　molecules　shifted　from　triazine　ring　to　benzene　ring,　with　increased　adsorption　energy　(-0.21　vs.　-0.55　eV)　and　a　reduced　CO2　bond　angle　(156　degrees　vs.　139　degrees).　Furthermore,　the　CO2-to-CH4　pathway　was　thoroughly　clarified　based　upon　the　in-situ　DRIFTS　and　energy　barriers　calculations,　where　CTF-1　followed　the　formate　route　and　B-doped　CTF　utilized　the　water　gas　shift　reaction.　The　introduction　of　B　doping　lowered　energy　barrier　of　*CHO　formation　for　improving　CH4　selectivity.　This　study　offers　a　strategy　for　enhancing　product　selectivity　by　breaking　the　electronic　symmetry　of　photocatalysts.