The activity of single-crystal catalysts with different crystal faces varies greatly, and the construction of catalysts with highly exposed active facets is essential for the improvement of photocatalytic performance. In this paper, Cu₂O (100) crystal facets were transformed into high degrade-active Cu₂O (111) crystal facets by doping with halogen atoms Br for the photocatalytic degradation of tetracycline. The effect of the optimal Br/Cu₂O ratio on the degradation activity was investigated by adjusting the amount of Br. Meanwhile, based on photocatalytic degradation performance tests, photoelectric performance characterization and theoretical calculations, it was found that the doped Br-Cu₂O introduced impurity energy levels, reduced the band gap, broadened the absorption range of the photocatalyst under visible light, and enhanced the oxidation capacity and the rate of photogenerated electron leap. In addition, the highly active Cu₂O (111) crystal surface facilitates the adsorption of oxygen to generate superoxide radicals and promote the photocatalytic reaction. The synergistic effect of these two aspects promotes the efficient degradation of tetracycline by Br-Cu₂O. This work provides a promising idea for the design and construction of highly efficient active surface highly exposed photocatalysts.