Metal-free　conjugated　microporous　polymers　(CMPs)　as　visible-light　active　and　recyclable　photocatalysts　offer　a　green　and　sustainable　alternative　to　classical　metal-based　photosensitizers.　However,　the　strategy　for　screening　CMP-based　heterogeneous　photocatalysts　has　not　been　interpreted　up　to　now.　Herein,　we　present　a　general　strategy　for　obtaining　excellent　solid　photocatalysts,　which　is　to　implement　bandgap　engineering　in　the　same　series　of　materials.　As　a　proof　of　concept,　three　conjugated　porous　materials　containing　benzo[1,2-b:3,4-b′:5,6-b′′]trithiophene　building　blocks　(BTT-CMP1,　BTT-CMP2　and　BTT-CMP3)　were　successfully　constructed.　They　possess　permanent　porosity　with　a　large　specific　surface　area　and　excellent　stability.　By　changing　the　linker　between　benzotrithiophene　units,　the　bandgaps,　energy　levels　and　photoelectric　performances　including　the　absorption,　transient　photocurrent　responses　and　photocatalytic　performances　of　BTT-CMPs　could　be　handily　modulated.　Indeed,　BTT-CMP2　displayed　the　best　catalytic　activity　for　visible-light-induced　synthesis　of　benzimidazoles　among　the　three　CMP　materials,　even　higher　than　that　of　small　molecule　photocatalysts.　As　a　metal-free　photocatalyst,　interestingly,　the　screened　BTT-CMP2　also　showed　extensive　substrate　applicability　and　outstanding　recyclability.　Additionally,　we　have　the　opinion　that　this　strategy　will　prove　to　be　a　guiding　principle　for　screening　superior　CMP-based　photocatalysts　and　broaden　their　application　fields.　©　The　Royal　Society　of　Chemistry　2020.