Abstract: To address the limited understanding of how functional group loading affects the photocatalytic performance of covalent triazine polymers (CTPs), hydroxylated covalent triazine polymers (CTP-OH) were synthesized using 2,5-bis(4-cyanophenyl)thiazolo5,4-dthiazole (TT-BN) as the photoactive monomer. Three CTP-OH samples with different hydroxyl contents were prepared by adjusting the cyano molar ratio of the photoactive monomer to the hydroxyl-bearing monomer 4-(hydroxymethyl)benzonitrile (3∶1, 8∶1, and 18∶1), which were labeled as CTP-OH-3∶1, CTP-OH-8∶1, and CTP-OH-18∶1, respectively. The results demonstrated that CTP-OH-3∶1 with the highest hydroxyl content exhibited the strongest photocurrent response and the lowest interfacial charge-transfer resistance. Under blue-light irradiation, photocatalytic organic debromination over CTP-OH-3∶1 achieved a 67% isolated yield, outperforming the control samples CTP-OH-8∶1 (isolated yield of 53%) and CTP-OH-18∶1 (isolated yield of 50%). As the hydroxyl content increased, the capabilities of light absorption, exciton dissociation, and charge transport of CTP-OH were simultaneously enhanced, thereby effectively promoting the photocatalytic performance. This work achieves quantitative regulation of hydroxyl groups, elucidates the structure-activity relationship, and provides new insights for the design of conjugated polymer photocatalysts.