Metal　complex-based　photocatalysts　are　promising　for　CO2　reduction.　Their　catalytic　performances　greatly　rely　on　the　synergy　of　ligands　and　metal　ions.　Here,　we　demonstrate　an　assembly　of　covalent　organic　cage　(COC)　and　metal　ions　for　photocatalytic　CO2　reduction.　The　coordinated　metal　serves　as　catalytically　active　site　for　CO2　reduction,　while　the　cage　not　only　chelates　the　metal　site,　but　also　enhances　the　local　concentration　of　CO2　around　metal　site,　and　decreases　the　key　intermediate　reaction　energy　barrier,　thereby　promoting　the　CO2　reduction　reaction　kinetically　and　thermodynamically.　Accordingly,　a　Ni　metalized　COC　exhibited　outstanding　photocatalytic　performance　in　CO2-to-CO　conversion　under　visible　light　irradiation.　This　study　highlights　the　feasibility　and　advantage　of　organic　cages　for　the　construction　of　photocatalysts　for　artificial　photosynthesis.