Highly efficient photocatalyst is the demand for controlling environmental pollution, especially the toxic and refractory organic contaminants. Herein, a series of bismuth-rich Bi4O5BrxI2-x solid solution photocatalysts were prepared through a one-step solvothermal method by adjusting the molar ratio of Br/I, which can effectively degrade organic pollutants of phenol and Rhodamine B (RhB). The structure and morphology of the photocatalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM). The results indicated that Bi4O5BrxI2-x solid solution photocatalysts were successfully synthesized. The obtained samples showed superior photocatalytic activities toward phenol and RhB under visible light irradiation. Besides, the photocatalytic performances can be optimized by changing the ratio of Br/I. When the ratio of Br/I was 1:1, the obtained Bi4O5BrxI2-x solid solution exhibited the highest photocatalytic performance, which was nearly 6.4 and 8.5 times higher than that of pure Bi4O5Br2 and Bi4O5I2 for phenol degradation, respectively. The enhancement can be ascribed to the high efficient separation of photogenerated electron-hole pairs in Bi4O5BrxI2-x solid solution, which was confirmed by the corresponding optical and photoelectrochemical characterizations.