The g-C3N4-Cu2O (CNCu2O-G) with a p-n heterojunction structure in the presence of glutamate was successfully developed through hydrothermal synthesis and high-temperature calcination. When addition the glutamate, the surface morphology of the heterojunction was regulated, and its specific surface area increased by a factor of approximately 1.5, and reaction sites were increased. Additionally, the charge recombination rate of the heterojunction was reduced, and the absorption band was red-shifted to 460 nm, leading to stronger heterostructure contact interfaces, thus the visible-light utilization efficiency was enhanced. The catalytic performance of the CNCu2O-G was very stable, with no significant change in the photocatalytic efficiency of CNCu2O-G after six recycles, the Fourier transform infrared patterns and X-ray diffraction of CNCu2O-G exhibited no significant changes after the photocatalytic reaction. Furthermore, electron paramagnetic resonance and free-radical removal experiments indicated that the holes and superoxide radicals were dominant species during the reaction.