With the development of industrialization and modernization, water pollution has become increasingly serious, and the use of sunlight for water pollution degradation has become a future development trend. In this paper, flower?like BiOI photocatalyst was prepared via a solution route at room temperature without any template, and characterized by X?ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV?Vis diffuse reflectance spectra (UV?Vis DRS). As?synthesized flower?like BiOI showed better visible light photocatalytic activity for degrading Rhodamine B (RhB) than TiO₂. The experimental results of active species and electron spin resonance (ESR) measurement showed that ·O {}_{\mathrm{2}}^{-} was the main active species in the photocatalytic degraded process of organic pollutant over flower?like BiOI, and the possible degradation mechanism was speculated. This study provides a simple and convenient synthesis method for high activity photocatalysts.