The ternary magnetic Fe₃O₄/BiOBr/BiOI (x : 3 : 1) photocatalysts were successfully synthesized by a facile solvothermal method. The samples were characterized by XRD, SEM, EDS, ICP-AES, XPS, UV-vis DRS, PL and VSM. Nitrogen-containing dye RhB was used as a degradation substrate to evaluate the photocatalytic degradation activities of the samples. The photocatalytic performance of Fe₃O₄/BiOBr/BiOI (0.4 : 3 : 1) is superior to other Fe₃O₄/BiOBr/BiOI (x : 3 : 1). Compared with binary magnetic Fe₃O₄/BiOBr (0.5 : 1) prepared in our previous work, the Fe₃O₄/BiOBr/BiOI (0.4 : 3 : 1) has obvious advantages in photocatalytic activity and adsorption capacity. And the specific surface area (48.30 m² g⁻¹) is much larger than that of the previous report (Fe₃O₄/BiOBr/BiOI (0.5 : 2 : 2)) synthesized by a co-precipitation method. Besides, after 25 s of magnetic field, Fe₃O₄/BiOBr/BiOI (0.4 : 3 : 1) can be rapidly separated from water. After eight recycling cycles, the magnetic properties, photocatalytic activity, crystallization and morphology of the Fe₃O₄/BiOBr/BiOI (0.4 : 3 : 1) catalyst remain good. The possible photocatalytic degradation mechanism of RhB under Fe₃O₄/BiOBr/BiOI (0.4 : 3 : 1) photocatalyst was also proposed. The results indicate that the ternary magnetic Fe₃O₄/BiOBr/BiOI (0.4 : 3 : 1) composite with high photocatalytic degradation efficiency, good magnetic separation performance and excellent recyclability and stability has potential application prospect in wastewater.