The development of high-performance visible-light photocatalysts with a tunable band gap has great significance for enabling wide-band-gap (WBG) semiconductors visible-light sensitive activity and precisely tailoring their optical properties and photocatalytic performance. In this work we demonstrate the continuously adjustable band gap and visible-light photocatalysis activation of WBG BiOIO₃via iodine surface modification. The iodine modified BiOIO₃ was developed through a facile in situ reduction route by applying BiOIO₃ as the self-sacrifice template and glucose as the reducing agent. By manipulating the glucose concentration, the band gap of the as-prepared modified BiOIO₃ could be orderly narrowed by generation of the impurity or defect energy level close to the conduction band, thus endowing it with a visible light activity. The photocatalytic assessments uncovered that, in contrast to pristine BiOIO₃, the modified BiOIO₃ presents significantly boosted photocatalytic properties for the degradation of both liquid and gaseous contaminants, including Rhodamine B (RhB), methyl orange (MO), and ppb-level NO under visible light. Additionally, the band structure evolution as well as photocatalysis mechanism triggered by the iodine surface modification is investigated in detail. This study not only provides a novel iodine surface-modified BiOIO₃ for environmental application, but also provides a facile and general way to develop highly efficient visible-light photocatalysts.