Poor light utilization and charge separation are the major factors that retard performance of g-C3N4 and solar conversion application to green energy. Herein, with the aim to address these issues and enhance photocatalytic hydrogen performance, we design and synthesize the modified g-C3N4 via defect assemblage of cyano group and carbonyl group. Cyano group and carbonyl group linked in the apex of heptazine unit were loaded into g-C3N4 framework, endowing g-C3N4 with extended light response range, tunable band structure and fast charge separation. By experiments analysis and theoretical calculations, the such a defect assemblage can attract photo-charge from other parts of heptazine unit and serve as active sites in photocatalytic process. Therefore, the modified g-C3N4 material show a ten times higher photocatalytic hydrogen amount than the pristine one and the corresponding apparent quantum efficiency under 405 and 420 nm are 32.30 % and 17.94 %, respectively. In this work, the defect assemblage into g-C3N4 shows the potential of synergistic effect of different defects on enhancing photocatalytic performance, which can pave a new avenue for the defect engineering in photocatalysis.