Defect engineering is a versatile approach to modulate band and electronic structures as well as materials performance. Nowadays, more research has been performed for enhancing catalytic performance of organic photocatalysts via the regulation of structure defect. Herein, we constructed the dibenzo[b,d]thiophene-sulfone-based conjugated microporous polymers (CMPs) with alkynyl defects via the molecular design. The effects of the concentration of alkynyl defects on the optical band gap, energy level structure, charge separation and photoactivity of the as-prepared samples were further explored. Combination of the first-principle density functional theory (DFT) calculations and experimental results, the incorporation of alkynyl defects accelerated the separation of photogenerated charge carriers. Furthermore, the concentration of alkynyl defects in CMPs can be adjusted by the dosage of 1,3-diethynylbenzene (MEB), thereby modulating the electronic structure and charge carrier separation properties. At appropriate alkynyl defect concentration, the prepared Defect-TD-2 shows higher visible-light photocatalytic performance for H₂ production and pollutants degradation. The work therefore shows an efficient self-modification strategy for improving the photoactivity of CMPs.