In this paper, Cu-doped Bi₂WO₆ was synthesized via a solvothermal method and applied it in photocatalytic N₂ immobilization. Characterization results showed the presence of a small amount of metallic Bi in the photocatalyst, indicating that the synthesized photocatalyst is actually Bi/Cu-Bi₂WO₆ composite. The doped Cu had a valence state of +2 and most likely substituted the position of Bi³⁺. The introduced Cu did not affect the metallic Bi content, but mainly influenced the energy band structure of Bi₂WO₆. The band gap was slightly narrowed, the conduction band was elevated, and the work function was reduced. The reduced work function improved the transfer and separation of charge carriers, which mainly caused the increased photoactivity. The optimized NH₃ generation rates of Bi/Cu-Bi₂WO₆ reached 624 and 243 μmol·L^–1·g^–1·h^–1 under simulated solar and visible light, and these values were approximately 2.8 and 5.9 times higher those of Bi/Bi₂WO₆, respectively. This research provides a method for improving the photocatalytic N₂ fixation and may provide more information on the design and preparation of heteroatom-doped semiconductor photocatalysts for N₂-to-NH₃ conversion.