Reinforcing migration of charge carrier in g-C3N4 photocatalytic system is critical for photocatalytic H-2 evolution. Herein, we constructed a benzene-ring-incorporated g-C3N4 by copolymerization of urea with N-phenylthiourea. A electron donor-acceptor conjugated structure is formed in which benzene ring is the donor while triazine ring is the acceptor. It is noteworthy that ultrafast transient absorption spectroscopy and density functional theory calculation were applied to gain more insight into the properties of the benzene ring with g-C3N4 as the electron donor in the triazine ring. As expected, the introduction of the benzene ring into triazine ring of the g-C3N4 displayed extraordinarily aggrandized hydrogen evolution, which not only crucially modified the pi electronic structures and promote pi-electron availability, but also played the role of a donor to improve the electron-hole separation. This study revealed that the photocatalytic H-2 evolution of the donor-acceptor system can be further improved by inserting suitable pi-conjugated as one of the units. (C) 2020 Elsevier Ltd. All rights reserved.