In-situ photocatalytic H₂O₂ production has been receiving increasing attention in recent years for sustainable H₂O₂ synthesis. Graphitic carbon nitride (g-C₃N₄) is regarded as one of the most promising semiconductor photocatalysts for H₂O₂ evolution. Introducing N defects in g-C₃N₄ has been proved to be an effective strategy to enhance photocatalytic activity. However, the photocatalytic mechanism of the N vacancies is ambiguous and different types of N vacancies in g-C₃N₄ may exhibit different effects on photocatalytic activity. Herein, we develop a facile sodium persulfate eutectic polymerization method to prepare the g-C₃N₄ with abundant three coordinate nitrogen (N3_C) vacancies. This type of nitrogen vacancy has not been studied in g-C₃N₄ for photocatalytic H₂O₂ production. Our results showed that the introduction of N3C vacancies in the g-C₃N₄ successfully broadened the light absorption range, inhibited the photoexcited charge recombination with enhanced O₂ adsorption to promote oxygen activation. The photocatalytic H₂O₂ evolution from the N3_C-rich g-C₃N₄ is 4.5 times higher than that of the pristine g-C₃N₄. This study demonstrates a novel strategy to introduce N3C vacancies in g-C3N4, which offers a new method to develop active catalysts for photocatalytic H₂O₂ evolution.