Abstract: The pollution of pesticides seriously threatens the ecological environment and drinking water safety. A novel and efficient photocatalyst of BiOI/BiOBr_0.9I_0.1 was prepared through solvothermal method. The physicochemical properties, such as structure, morphology and optical properties, were characterized by detections of XRD, SEM, XPS, UV-vis DRS, PL, EIS, etc. The BiOI/BiOBr_0.9I_0.1 synthesized has a cluster-like accumulation structure, which facilitates the increase of active sites. The combination of solid solution and heterojunction broadens the photoresponse range of BiOBr, effectively prevents the recombination of photogenerated electron-hole pairs inside BiOI/BiOBr_0.9I_0.1 and improves the redox ability of photogenerated carriers. The results of photocatalytic experiments show that 15wt%BiOI/BiOBr_0.9I_0.1 reaches the best photocatalytic performance for 2,4-dichlorophenoxyacetic acid (2,4-D) under visible light, and the degradation efficiency of 2,4-D can reach 95% within 120 min. Furthermore, the degradation rate still reaches 80.9% after four cycles of experiments. According to the results of capture experiments and electron spin-resonance (ESR) tests, it can be confirmed that •O₂⁻ and h⁺ are the main active species. The BiOBr_0.9I_0.1 synthesized can effectively modulate the energy band structure of BiOBr. The heterojunction composed of BiOBr_0.9I_0.1 and BiOI is consistent with the characteristics of Z-scheme heterojunction, and the synergistic effect between the two strategies of constructing heterojunction and solid solution can be produced in enhancing the photocatalytic activity of BiOBr.