Cl-incorporated BiOI nanostructures with different Cl/I molar ratios have been successfully fabricated via a facile room temperature method in H2O/EG mixture solvent. Combined with FTIR, Raman spectrum, XRD Rietveld refinements, and DFT calculation) the incorporated Cl ions are found mainly occupied on I sites, resulting in a hybrid valence band consisting of I 5p, O 2p, and Cl 3p orbitals, which deepens the valence band location of the materials and induces photogenerated holes with higher oxidation power. The incorporated Cl ions into the lattice also change the evolution of photogenerated electrons and, holes, inducing the broadening of the bandgap but efficient production of photogenerated carriers. The enhanced oxidation power of Cl-incorporated BiOI products was evaluated by photocatalysis degradation of methylene blue, an organic dye for which pure BiOI shows negligible direct oxidation efficiency. Ascribed to the relatively low valence band maximum (VBM) and efficient generation of photoinduced electrons and holes, the incorporated products show distinct enhancement photocatalytic activities.