The　visible-light-driven　photocatalytic　CO2　reduction　with　high　efficiency　is　highly　desirable　but　challenging.　Herein,　we　present　porphyrin-tetraphenylethene-based　covalent　organic　frameworks　(MP-TPE-COF,　where　M=H2,　Co　and　Ni;　TPE=4,4′,4″,4-(ethane-1,1,2,2-tetrayl)　tetrabenzaldehyde;　COF=covalent　organic　framework)　as　ideal　platforms　for　understanding　photocatalytic　CO2　reduction　at　molecular　level.　Experimental　and　theoretical　investigations　have　demonstrated　crucial　roles　of　metalloporphyrin　units　in　selective　adsorption,　activation　and　conversion　of　CO2　as　well　as　in　the　separation　of　charge　carriers　and　electron　transfer,　thus　allowing　for　flexible　modulation　of　photocatalytic　activity　and　selectivity.　CoP-TPE-COF　exhibits　high　CO　evolution　rate　of　2,414　µmol　g−1　h−1　with　the　selectivity　of　61%　over　H2　generation　under　visible-light　irradiation,　while　NiP-TPE-COF　provides　CO　evolution　rate　of　525　µmol　g−1　h−1　and　93%　selectivity　with　superior　durability.　Moreover,　the　photocatalytic　system　is　feasible　for　the　simulated　flue　gas,　which　provides　CO　evolution　rate　of　386　µmol　g−1　h−1　and　selectivity　of　77%.　This　work　provides　in-depth　insight　into　the　structure-activity　relationships　toward　the　activation　and　photoreduction　of　CO2.　©　2020,　Science　China　Press　and　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.