Abstract: Bi-based materials have attracted much attention due to their broad light response and stable photocatalytic properties. However, their high recombination rate of photoinduced electron-hole pairs and low photocatalytic efficiency remain common drawbacks. The fabrication of heterojunction materials has proven to be an efficient strategy for the resolution of these issues. Herein, flower-shaped BiOAc was synthesized by chemical precipitation at room temperature. Subsequently, BiOAc/BiOX (X=Cl, Br) composite materials were synthesized through ion exchange between BiOAc and BiOX. The crystalline structures and optical properties of the materials, as well as the recombination of photoinduced carriers were characterized by XRD, SEM, TEM, N₂ adsorption and desorption isotherm, UV-vis DRS, and EIS. Mixed cationic dyes (rhodamine B (RhB) and methylene blue (MB)) and anionic dyes (Isatin and Titan yellow) were selected as target pollutants to evaluate the photocatalytic performance and stability of the samples. In addition, trapping experiments were conducted to detect the reactive species in the BiOAc/BiOX photocatalytic system, and the possible functional mechanism was proposed. Conclusions were obtained as the following: (1) A BiOAc/BiOX heterojunction was formed through the ion-exchange process. (2) When the molar ratio of BiOAc to BiOX was 6:1, the best photocatalytic performance was obtained. (3) The BiOAc/BiOBr exhibited a stronger adsorption capacity for cationic dyes than BiOAc/BiOCl, which facilitated the photocatalytic degradation of the pollutants. (4) Cycling experiments revealed that the prepared BiOAc/BiOX composites had excellent photocatalytic stability. (5) The main species in the photocatalytic reaction were ·O₂^- and h⁺. The transfer of photoinduced electrons between the BiOAc and BiOX conduction bands inhibited the recombination of electron-hole pairs, thus improving the photocatalytic activities. The research results suggested that the prepared materials had strong potential for advanced treatment of dye wastewater.