Polymeric　semiconductors　are　emerging　as　a　kind　of　competitive　photocatalysts　for　hydrogen　evolution　due　to　their　well-tunable　structures,　versatile　functionalization,　and　low-cost　processibility.　In　this　work,　a　series　of　conjugated　porous　polymers　with　substantial　cyano-substituted　fully　sp　2　-carbon　frameworks　are　efficiently　synthesized　by　using　electron-deficient　tricyanomesitylene　as　a　key　building　block　to　promote　an　organic　base-catalyzed　Knoevenagel　condensation　with　various　aldehyde-substituted　arenes.　The　resulting　porous　polymers　feature　donor-acceptor　structures　with　π-extended　conjugation,　rendering　them　with　distinct　semiconducting　properties.　They　possess　hierarchically　porous　structures,　nanoscale　morphologies,　and　intriguing　wettability.　These　promising　physical　characters,　finely　tailorable　by　varying　the　arene　units,　are　essentially　relevant　to　the　abundant　cynao　substituents　over　the　whole　frameworks.　The　as-prepared　porous　polymers　exhibit　excellent　visible-light-driven　photocatalytic　activity　for　water-splitting　hydrogen　evolution　with　apparent　quantum　yield　up　to　2.0%　at　420　nm　or　1.9%　at　470　nm,　among　the　highest　values　yet　reported　for　porous　polymer-based　photocatalysts,　also　representing　the　first　example　of　such　kinds　of　catalysts　formed　through　a　metal-free-catalyzed　carbon–carbon　coupling　reaction.　©　2017　WILEY-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim