Many studies have been devoted to enhancing photocatalytic activity of hydrogen generation by water splitting in recent years. Herein, a well-defined 3D flowerlike mesoporous photocatalyst (kermesinus BiOI, K-BiOI) was successfully prepared through UV-Vis-Light driving method. The X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) and surface photovoltage (SPV) tests confirmed that the oxygen vacancies (OVs) were introduced onto the surface of BiOI, which resulted that the color of BiOI changed from normal orange to kermesinus. The successful introduction of OVs led to the absorption range of K-BiOI stretched. Although the OVs are introduced on the surface, the main body of the material is still BiOI. Furthermore, K-BiOI exhibited a remarkably improved hydrogen production rate of 6.51 mmol g^-1 h^-1 under UV-Vis-light irradiation, which was 21-fold higher than that of BiOI under UV light irradiation. The OVs on the K-BiOI surface could form a defect state lying near the conduction band minimum of the photocatalyst and act as an electron scavenger delaying the photogenerated carrier recombination during the photoreaction process. The present work provides a new approach to introduce OVs on the surface of BiOI, which can provide a new strategy of catalyst preparation for the efficient H₂ production.