Heterojunction　engineering　is　a　powerful　approach　for　improving　the　separation　efficiency　of　photogenerated　charge　carriers.　In　this　study,　ultrathin　2D/2D　CeVO4/WO3　center　dot　H2O　heterojunction　nanosheets　are　synthesized　via　electrostatic　self-assembly　of　ultrathin　CeVO4　(similar　to　1.3　nm)　and　WO3　center　dot　H2O　(similar　to　2.4　nm)　nanosheets　for　greatly　enhancing　photocatalytic　CO2　reduction　and　H2O　oxidation　performance.　The　2D　heterojunction　nanosheets　process　a　Z-scheme　charge　transfer　pathway　to　effectively　promote　charge　separation　efficiency　and　superior　redox　capabilities.　Concurrently,　the　ultrathin　heterojunction　configuration　substantially　reduces　the　migration　distance　of　charge　carriers.　These　synergistic　effects　endow　the　CeVO4/WO3　center　dot　H2O　composite　with　the　marked　CH4　and　CO　production　rates　of　8.4　mu　mol　center　dot　g(-1)center　dot　h(-1)　and　38.5　mu　mol　center　dot　g(-1)center　dot　h(-1)　under　full-spectrum　illumination.　The　CO　generation　rate　of　the　ultrathin　heterojunction　surpasses　pure　WO3　center　dot　H2O　by　similar　to　32　times　and　CeVO4　by　similar　to　18　times.　This　study　also　provides　insights　into　the　rational　design　of　heterojunction　nanosheet　photocatalysts　for　CO2　reduction　with　H2O.