Low-mass　interfacial　contacts　and　poor　charge　transfer　efficiency　severely　limit　the　CO2　photoreduction　performance　of　semiconductor　heterojunctions.　In　this　work,　g-C3N4/Ag@Ag3PO4　S-scheme　heterojunction　is　prepared　by　an　in-situ　growth　method.　The　main　product　for　CO2　photoreduction　is　CO　with　the　selectivity　of　97　%.　The　evolution　rate　of　CO　for　optimal　g-C3N4/Ag@Ag3PO4　heterojunction　is　123.8　μmol　g−1　h−1,　which　are　8.3-and　3.4-fold　higher　than　those　of　pristine　Ag3PO4　and　g-C3N4,　respectively.　It　is　found　that　Ag3PO4,　Ag,　and　g-C3N4　form　strong　interacting　interfacial　structure,　in　which　Ag3PO4　links　with　Ag　nanoparticles　through　tandem　Ohmic　contact.　More　importantly,　σ　bonds　are　formed　via　hybridization　of　px　orbital　for　C　and　N　with　dx2-y2　orbitals　of　Ag　in　g-C3N4/Ag@Ag3PO4　S-scheme　heterojunction,　establishing　an　atomic-level　dx2-y2(Ag)-px(C,N)　charge　flow　highway.　This　work　provides　new　viewpoints　into　the　design　of　heterojunction　photocatalysts　with　high-quality　interfaces　and　highlights　the　insights　of　charge　transfer　behavior　in　regulating　the　catalytic　activity.　©　2024