Bismuth oxyhalide (BiOX) photocatalysts have attracted tremendous attentions due to their unique optical and electronic properties. However, pristine BiOX suffered from inherent drawbacks and unsatisfactory photocatalytic performance. Interest in engineering layered structure BiOX for efficient environment remediation has grown exponentially. Recent studies tend to focus on alloying, bismuth-rich strategies, defect introduction, element doping. Therefore, the aim of this review is to summarize multiply structural optimized strategies for the improvement of their photocatalytic applications in environmental remediation. The distinct photochemical properties and synthesis method of alloyed, bismuth-rich, doped and defect-introduced BiOX are detailly elaborated based on the discussion of the structure-property relationship. The other methods such as heterojunction, facet effect, surface plasmonic resonance and strain engineering are briefly introduced. Subsequently, environmental applications in aquatic pollutants photodegradation and air purification are also discussed. Finally, challenges and outlooks covering synthetic strategies, characterization, and applications are featured.