Abstract: Recently, a new carbon nitride (C₃N₅) photocatalyst has attracted much attention due to its excellent light harvesting and unique 2D structure. However, high recombination rates of electron-hole pairs of bulk C₃N₅ serious affect the photocatalytic performance. Herein, nickel oxide (NiO) modified C₃N₅ p-n junctions photocatalyst was synthesized by a facile hydrothermal method. Results indicated that the 9-Ni/C₃N₅ nanosheet photocatalyst showed excellent hydrogen production efficiency under visible light. The hydrogen production rate reached 357 μmol/(g·h), which was 107-fold higher than that of pristine C₃N₅. The high catalytic performace was attributed to the 9-Ni/C₃N₅ p-n junctions which could efficiently promote photogenerated electron-hole pair separation and thus promote the hydrogen evolution reaction.