Photocatalytic　CO2　reduction　reaction　(CO2RR)　is　an　effective　pathway　for　high　value-added　chemicals.　Poly　(triazine　imides)　(PTI)　have　a　great　potential　for　photocatalytic　CO2RR　due　to　its　high　crystallinity.　We　have　codoped　PTI　with　nonmetals　B　and　S,　in　which　the　charge　compensation　between　B　and　S　forms　a　shallow　＂donor-acceptor　pair＂.　The　charge　compensation　effect　regulates　the　polarity　of　Lewis　acid-base　pairs　so　that　more　electrons　localize　in　the　pyridine　N,　which　facilitates　the　CO2　hydrogenation　and　improves　both　the　activity　and　the　selectivity　of　CO2RR　to　CO.　Furthermore,　the　hydrogen　source　of　the　reaction　is　the　adsorbed　H*　rather　than　the　substrate　H　from　PTI.　Through　the　nonadiabatic　molecular　dynamics　simulations,　although　B　and　S　codoping　PTI　(B-S1/PTI)　has　a　larger　nonadiabatic　coupling　and　a　narrower　energy　gap　than　B　doping　PTI　(B/PTI),　a　fast　decoherence　rate　prolongs　the　nonradiative　recombination　time　and　carrier　lifetime　of　B-S1/PTI,　which　improves　its　catalytic　efficiency　of　CO2RR.　This　work　reveals　that　the　charge　compensation　effect　of　nonmetals　enhances　the　photocatalytic　CO2RR　performance　and　prolongs　the　charge　carrier　lifetime.