Despite the fact that close correlation has been established between the structures of covalent organic frameworks (COFs) and their photocatalytic properties, the effect of COF isomerism has been rarely studied so far due to the limited number of isomeric precursors available for the synthesis of COF isomers. In this study, regioisomeric benzotriazole-based COFs were prepared, with the alkyl substituent group located at the middle or side nitrogen. In spite of possessing an identical molecular formula, the COF isomers showed distinct photophysical and electrochemical properties. When serving as photocatalysts, the symmetric COF isomer exhibited a hydrogen evolution rate up to 24.21 mmol h–1 g–1 under natural outdoor conditions or 19.77 mmol h–1 g–1 under simulated visual light irradiation, which was much higher than the asymmetrical isomer. This study enriches the family of imine-linked COFs and provides insights into the photocatalysis mechanism from a subtle perspective of regioisomers.