This review discusses the trends in alloying engineering for BiOX-based photocatalysts. BiOX (Cl, Br, I) is a layered semiconductor with unique properties, but its photocatalytic performance is limited by its band gap and carrier separation efficiency. Alloying engineering is used to optimize these properties by modifying the structure and electronic properties of BiOX. The review covers the structure of BiOX, the effects of alloying on energy band structure and carrier behavior, and various modification methods such as defect engineering, morphology control, and synergistic approaches like bismuth-rich strategies, cation doping, heterojunction construction, and plasma resonance effects. Applications of alloyed BiOX in energy and environmental fields, including contaminant degradation, antibacterial activity, CO₂ reduction, nitrogen fixation, and organic synthesis, are summarized. The review also discusses current challenges and future directions for alloyed BiOX. It is expected that this work will provide guidance for further study of alloying engineering to optimize intrinsic properties and design more efficient photocatalysts. BiOX materials were first discovered in the early 19th century and have since been widely used in photocatalysis. Their layered structure facilitates polarization of atomic orbitals and the generation of built-in electric fields, which enhances carrier separation and migration. However, intrinsic defects limit their photocatalytic activity. Alloying engineering, which involves dissolving solute atoms in the solvent lattice without changing the solvent structure, can adjust the position of the valence and conduction bands, affecting the forbidden band width and redox capability. Alloying can also introduce electron capture centers, facilitating carrier separation. By controlling the ratio of different halogens in the alloy phase, the electronic structure and morphology of the material can be adjusted, improving photocatalytic performance. Recent research has shown that alloying BiOX can achieve continuous adjustment of the energy band structure, leading to an optimal balance of light absorption and redox capacity. This review provides a comprehensive overview of the synthesis methods, properties, and applications of alloyed BiOX, highlighting the importance of alloying engineering in improving photocatalytic performance.This review discusses the trends in alloying engineering for BiOX-based photocatalysts. BiOX (Cl, Br, I) is a layered semiconductor with unique properties, but its photocatalytic performance is limited by its band gap and carrier separation efficiency. Alloying engineering is used to optimize these properties by modifying the structure and electronic properties of BiOX. The review covers the structure of BiOX, the effects of alloying on energy band structure and carrier behavior, and various modification methods such as defect engineering, morphology control, and synergistic approaches like bismuth-rich strategies, cation doping, heterojunction construction, and plasma resonance effects. Applications of alloyed BiOX in energy and environmental fields, including contaminant degradation, antibacterial activity, CO₂ reduction, nitrogen fixation, and organic synthesis, are summarized. The review also discusses current challenges and future directions for alloyed BiOX. It is expected that this work will provide guidance for further study of alloying engineering to optimize intrinsic properties and design more efficient photocatalysts. BiOX materials were first discovered in the early 19th century and have since been widely used in photocatalysis. Their layered structure facilitates polarization of atomic orbitals and the generation of built-in electric fields, which enhances carrier separation and migration. However, intrinsic defects limit their photocatalytic activity. Alloying engineering, which involves dissolving solute atoms in the solvent lattice without changing the solvent structure, can adjust the position of the valence and conduction bands, affecting the forbidden band width and redox capability. Alloying can also introduce electron capture centers, facilitating carrier separation. By controlling the ratio of different halogens in the alloy phase, the electronic structure and morphology of the material can be adjusted, improving photocatalytic performance. Recent research has shown that alloying BiOX can achieve continuous adjustment of the energy band structure, leading to an optimal balance of light absorption and redox capacity. This review provides a comprehensive overview of the synthesis methods, properties, and applications of alloyed BiOX, highlighting the importance of alloying engineering in improving photocatalytic performance.