Nickel, a non-noble metal, is one of the most promising candidates for photocatalysis because it is inexpensive and an earth-abundant metal. Herein, Ni/CM-C₃N₄ nanocomposites with Ni as a cocatalyst were synthesized by a simple solvothermal method. Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed that Ni nanoparticles were loaded onto the surface of CM-C₃N₄. The prepared Ni/CM-C₃N₄ nanocomposites exhibited an enhanced hydrogen evolution activity. The most active catalyst contained 10% Ni and produced H₂ at a rate of 313.2 μmol h⁻¹ g⁻¹, which was obviously higher than that of pure CM-C₃N₄. The results of photoluminescence (PL) and photoacoustics (PA) studies indicated that the recombination efficiency of photo-induced electron–hole pairs was decreased for CM-Ni10 as compared to that for unmodified CM-C₃N₄. The transient photovoltage (TPV) measurements directly demonstrated that the recombination time of electron–hole pairs in CM-Ni10 was prolonged. More importantly, the reversed surface photovoltage (SPV) and the declined surface photocurrent (SPC) response of CM-Ni10 revealed that the photogenerated electrons could be trapped by Ni, leading to a better separation efficiency and a superior hydrogen production. Finally, the possible mechanism is proposed to illuminate the photogenerated charge behavior between CM-C₃N₄ and Ni, which might provide a theoretical basis to develop efficient cocatalysts for photocatalytic water splitting.