Iodine-incorporated BiOCl (I–BiOCl) core–shell microspheres were for the first time fabricated using a one-step approach under atmospheric pressure. The morphology and compositional characteristics of the 3D hierarchitectures (HAs) of BiOCl were investigated by various techniques such as XRD, FESEM, TEM, EDS, XPS and PL. On the basis of observing the structure of BiOCl and iodine-containing BiOCl at different intervals of reaction time, a three-stage growth mechanism that involves an initial Ostwald ripening process followed by a self-assembly process is proposed. Meanwhile, iodine anions were utilized as both structure-directing agents for fabricating hollow, core–shell, solid structure and doped ions incorporated into the framework of the core–shell BiOCl spheres to extend the light adsorption edge to the visible light region. UV-vis spectra reveal that the band energies of the iodine anions-modified BiOCl (I–BiOCl) hierarchical hollow, core–shell, and solid samples (2.43 eV, 2.28 eV and 2.04 eV, respectively) exhibit obvious red-shifts with respect to that of the pure hollow BiOCl sample (3.23 eV). I–BiOCl without adding poly(vinylpyrrolidone) (PVP) was researched. This result demonstrated that the formation of the core–shell structure is induced by a synergetic effect by iodine and PVP. The specific surface area and porosity of the iodine anions-modified hierarchical BiOCl were also investigated by using nitrogen adsorption–desorption isotherms. The as-prepared I–BiOCl core–shell microspheres showed much higher photocatalytic activity than that of the reported TiO_2−x−yN_xF_y(SC)-3 and Bi₂WO₆, which was evaluated by the degradation of phenol under visible light (λ > 420 nm) and Rhodamine-B (RhB) dye under visible light (λ > 420 nm) and sun-light irradiation.