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 realizes quantitative regulation of hydroxyl groups, elucidates the structure–activity relationship, and provides new insights for the design of conjugated polymer photocatalysts.