By virtue of visible light absorption ability, the energy band structure and electronic affinity of covalent organic frameworks (COFs) can be easily tuned at the molecular level, making them attractive photocatalysts for metal-free organic transformation. However, the relationship between the electronic structure and photocatalytic properties of COFs is still vague. In this study, we developed a bottom-up strategy to construct three triazine-based COFs with different electronic structures through introducing various building blocks. The photocatalytic oxidation of sulfides to sulfoxides showed that electron-deficient COF afforded higher conversion and selectivity than that of electron-rich or neutral structures, which due to the electron-deficient triazine-based COF can not only facilitate the generation and separation of charge, but also enrich the photocatalytic active sites. This result was further confirmed by photoelectrochemical measurements and theoretical calculations. This work lights up the design and application of high-efficient metal-free photocatalysts by modulation of electronic structures.