In this study, we constructed a Z-scheme photocatalyst BiOCl-Ag-AgBr for the first time, with the aim of simultaneously removing the heavy metal Cr⁶⁺ ions and organic pollutant phenol in waste water. It was found that Ag nanoparticles (NPs) were selectively deposited on the {001} facets of BiOCl nanosheets in the process of photoreduction, and the outer layer of Ag NPs was further transformed into AgBr in the presence of Fe³⁺ and Br⁻. Compared with BiOCl and BiOCl-Ag, the ternary structure BiOCl-Ag-AgBr displays obviously higher photocatalytic activity for both Cr⁶⁺ reduction and phenol degradation. There exists a synergetic effect between Cr⁶⁺ ions and phenol for enhancing the photocatalytic activity of photocatalysts, i.e., the presence of Cr⁶⁺ ions can promote the degradation of phenol, while the existence of phenol also accelerates the reduction of Cr⁶⁺. The radical trapping experiments confirmed that BiOCl-Ag-AgBr is a Z-scheme semiconductor and all of e⁻, •O₂⁻, •OH, and h⁺ take part in the reactions of Cr⁶⁺ reduction and phenol degradation. The superior photocatalytic activity of BiOCl-Ag-AgBr should be ascribed to both its excellent sunlight response and the effective separation efficiency of photogenerated charge carriers with high redox ability.