2D　covalent　organic　frameworks　(COFs)　are　drawing　intense　attention　in　heterogenous　photocatalysis　due　to　their　porous,　crystalline,　and　tailor-made　structures.　For　highly　efficient　solar-to-chemical　energy　conversion,　revealing　and　modulating　active　centers　in　the　skeletons　of　COFs　are　of　great　importance　but　encounter　severe　challenges.　Herein,　it　is　demonstrated　that　cyano　conjugation　on　a　typical　β-ketoenamine-linked　COF　via　aldehyde-imine　Schiff-base　condensation　contributes　to　an　enhanced　stable　photocatalytic　H2-evolution　rate　of　1.8 mmol h−1　g−1　(λ ＞　420 nm)　with　a　superior　apparent　quantum　yield　of　2.12%　at　420 nm,　compared　to　pristine　COFs.　Both　experimental　results　and　density　functional　theory　calculations　disclose　that　the　cyano　conjugation　can　efficiently　improve　photoinduced　charge　separation　and　effectively　decrease　the　energy　barrier　for　H-intermediate　generation　on　the　carbonyl　oxygen　sites　of　the　functionalized　COFs.　These　findings　present　a　precise　organic　functionalization　strategy　to　optimize　active　centers　on　COF-based　photocatalysts　for　the　practical　applications.　©　2021　Wiley-VCH　GmbH