Carbon　nitrides　(g-C3N4)　have　emerged　as　the　promising　photocatalysts　for　CO2　conversion.　However,　they　suffer　from　inefficient　charge　transfer　and　a　lack　of　metal　sites.　Herein,　the　p-type　CoNiO2　nanosheets　are　anchored　on　the　n-type　g-C3N4　microtubes　to　construct　p–n　heterojunction　photocatalysts.　The　CoNiO2　nanosheets　provide　metal　sites　to　bind　and　activate　CO2　molecules,　and　the　configuration　of　p–n　heterojunction　impels　electron–hole　separation.　The　CoNiO2　nanosheets　that　are　vertically　aligned　on　the　surfaces　of　g-C3N4　microtubes　build　a　hierarchical　hollow　structure　and　an　intimate　contact　interface,　which　also　contributes　to　the　CO2　adsorption　and　rapid　migration　of　charged　carriers.　As　a　result,　the　g-C3N4@CoNiO2　p–n　heterojunction　photocatalysts　exhibit　outstanding　yields　(3645　μmol　h−1　g−1　of　CO　and　943　μmol　h−1　g−1　of　H2)　from　CO2　reduction　under　visible　light　irradiation,　much　higher　than　that　of　pure　CoNiO2　nanosheets　and　g-C3N4　microtubes.　In　situ　DRIFT　spectra　are　performed　to　monitor　the　intermediates　of　CO2　reduction　on　the　surfaces　of　g-C3N4@CoNiO2,　the　results　of　which　confirm　the　adsorption　and　activation　of　CO2　molecules.　It　is　expected　that　this　work　would　provide　a　feasible　strategy　for　designing　high-efficiency　g-C3N4-based　heterojunction　photocatalysts.　©　2021