Abstract: In order to improve the specific surface area and photocatalytic degradation ability of BiOI photocatalysts, three samples were prepared by solvothermal method: small pore spherical BiOI1 (solvent volume fraction of ethylene glycol is 100%, solvent volume fraction of ethanol is 0%), large pore spherical BiOI0.6 (solvent volume fraction of ethylene glycol is 60%, solvent volume fraction of ethanol is 40%), and mixed BiOI0.4 (solvent volume fraction of ethylene glycol is 40%, solvent volume fraction of ethanol is 60%). Through XRD, FT-IR and other characterizations, it was found that all three samples have a tetragonal BiOI structure. The formation of the BiOI0.6 macroporous structure is due to the synergistic effect of BiOI directional growth in ethylene glycol and rapid growth at low viscosity in ethanol. BiOI0.6 has a high BET specific surface area (154 m²/g), excellent BJH adsorption average pore size (18.5 nm), appropriate band gap (1.97 eV) and extremely low EIS impedance. Therefore, BiOI0.6 exhibited the best photocatalytic performance in the degradation of RhB.