g-C3N4 with π-delocalization was coordinated between urea and a small amount of 1,3,5-tris(4-aminophenyl)benzene (TAPB) (UCN-xTAPB) by a facile polymerization. Compared with pristine g-C3N4(UCN), the obtained materials, UCN-xTAPB, showed an extended delocalization with increased electrical conductivity, enhanced adsorption of visible light, and improved separation of photogenerated electron-hole pairs. The average H2 evolution rate of UCN-4TAPB is about 10.55 mmol h-1 g-1 under visible-light irradiation (λ > 420 nm), which is much higher than reported data. Furthermore, density-functional theory (DFT) calculation confirms that the proposed structure with the incorporation of TAPB into the CN network shows the extended delocalization. Moreover, different structures of aromatic rings (anthroic acid, naphthoic acid and benzoic acid) are applied to verify the role of the enhanced π-delocalization in g-C3N4. By adopting different precursors (thiourea, dicyandiamide) to polymerize with TAPB, we further confirm the extension of optical absorption under visible-light irradiation and the improvement of hydrogen evolution rate, indicating the universality of the current strategy. Therefore, we believe that our work provides an efficient strategy for constructing the delocalized structure of g-C3N4 as effective visible-light-responsive photocatalysts.