Conjugated　polymers　(CPs)　have　garnered　increasing　attention　in　the　field　of　photocatalysis　due　to　their　stability　and　molecular　tunability.　Understanding　the　structure–property　relationship　in　CPs　and　addressing　appropriate　molecular　design　strategies　are　pivotal　to　improving　the　photocatalytic　performance　of　CPs.　Herein,　a　new　efficient　cyano　(CN)　engineering　approach　was　proposed　to　promote　the　photocatalytic　performance　of　CPs,　and　three　representative　CP-based　photocatalysts　with　different　CN　contents　were　tailor-made　to　investigate　the　relationship　between　CN　functionalization　and　photocatalytic　activity.　A　series　of　systematically　experimental　and　theoretical　studies　reveal　that　CN　functionalization　contributes　to　strengthening　the　donor-acceptor　(D-A)　interaction,　enhancing　the　light　absorption　ability,　charge　separation/transfer　efficiency,　and　hydrophilicity　of　CPs,　and　also　facilitating　the　output　of　separated　photoinduced　electrons　from　CPs　to　Pt　cocatalyst.　Thus,　the　dicyano-functionalized　polymer　(P-2CN)　manifests　an　attractive　photocatalytic　performance　in　hydrogen　production.　This　study　provides　a　facile　strategy　to　develop　excellent　CP-based　photocatalysts　for　solar　fuel　production.　©　2022　Wiley-VCH　GmbH.