[en] Au nanoparticles (Au NPs) were deposited onto BiOCl_1−xBr_x nanosheets by using a facile ultrasonic treatment. The obtained Au-BiOCl_1−xBr_x composites exhibit excellent photocatalytic property in the reaction of decomposing phenol aqueous solution under simulated solar light irradiation. There is a positive relationship exists in the surface plasmon resonance (SPR) of Au NPs and enhanced activities, which is contributed to the separation of photo-induced electrons and holes as well as facilitate the absorption of visible light. In addition, the tunable energy band structure might be beneficial to enhance the photocatalytic activities of Au-BiOCl_1−xBr_x composites for optimizing the bandgap. And the ·OH and h⁺ species were the main active species in photocatalytic reactions. In this paper, the Au-BiOCl_1−xBr_x photocatalysts were demonstrated to be a promising material for practical applications in the purification of organic pollutants. - Highlights: • BiOCl_1-xBr_x with the decoration of Au NPs were successfully synthesized and characterized. • The band energy of Au-BiOCl_1-xBr_x can be tunable via solid-solution strategy. • The effect of surface plasmon resonance (SPR) was investigated. • The SPR effect could facilitate charge separation and extend the light absorption.