The g-C₃N₄ is considered to be a promising non-metallic semiconductor photocatalyst for converting CO₂ into value-added products. However, g-C₃N₄ undergoes recombination of photogenerated electrons and holes and its low CO₂ adsorption capacity. Here, g-C₃N₄ hollow microtube (TCN) structure with tunable N-vacancy concentrations (TCN-1) was controllably fabricated by hydrothermal self-assembly followed by H₂ heat treatment. The resultant N-vacancy with one-dimensional structure g-C₃N₄ exhibits excellent activity for photocatalytic CO₂ reduction, giving the CO generation rate of 7.06 μmol/g/h (TCN-1) under visible-light illumination without any co-catalyst or a sacrificial agent, which is 2.2- and 8.8- times that of TCN (3.12 μmol/g/h) and pristine g-C₃N₄ (0.75 μmol/g/h). It is well evidenced with experiments and DFT calculations that N-vacancy mainly originates from the selective cleavage of C=N–C sites on the surface of g-C₃N₄. The N-vacancy can act as electron trap, extending the lifetime of charge carriers. Moreover, the changes in the electron distribution around the vacancies thereby provide the driving force for the dissociation of excitons, which in turn promotes the activation of CO₂ adsorption. The bifunctional of g-C₃N₄ with structural optimization and defect design is a very promising candidate for enhancing the adsorption-activation of reactants and the carrier utilization of photocatalysts in the photocatalytic process.