Nitrogen photofixation using g-C3N4-based photocatalysts have attracted abundant of attentions recently. Herein, in this study, holey g-C3N4 (HGCN) nanosheets possess a good deal of carbon vacancies were prepared by means of thermally treating bulk g-C3N4 (BGCN) under an NH3 atmosphere. Characterization analysis revealed that the as-synthesized sample have identical crystal structure, larger BET specific surface area, stronger reduction capability, and higher photogenerated charge carrier separation rate than that of BGCN. These properties may contribute to enhance the nitrogen photofixation activity. It was also found that the rate of NH4+production for N2 photofixation of HGCN sample reached～25.54 mg L-1 h-1 g-1cat, which is approximately～5.87 times higher than that of BGCN sample under optimal reactive conditions. Moreover, a plausible mechanism of HGCN for nitrogen photofixation process was illuminated in detail.