Graphitic carbon nitride (g-C3N4) as a novel photocatalyst with great potentials has been extensively employed in solar-driven energy conversion. Herein, the novel in situ g-C3N4 p-n homojunction photocatalyst with nitrogen vacancies (NV-g-C3N4) is successfully fabricated via hydrothermal synthesis followed by two-step calcination. The in situ NV-g-C3N4 homojunction can be employed as an effective photocatalyst for hydrogen generation through water splitting under visible light, and the optimum rate constant of 3259.1 mu mol.g(-1).h(-1) is achieved, which is 8.7 times as high as that of pristine g-C3N4. Moreover, the markedly increased photocatalytic performance is ascribed to the enhanced light utilization, large specific surface area and unique nitrogen-vacated p-n homojunction structure, which provides more active sites and improves the separation of photo-excited electron-hole pairs. Besides, the underlying mechanism for efficient charge transportation and separation is also proposed. This work demonstrates that the remodeling of g-C3N4 p-n homojunction with nitrogen vacancies is a feasible way as highly efficient photocatalysts and might inspire some new strategies for energy and environmental applications. (c) 2020 Elsevier Inc. All rights reserved.