In this work, the geometrical configuration, electronic structure, optical properties and charge transfer behavior of BiOBr001 surface with three different atomic exposure terminations (-BiO, -1Br and -2Br) and single-atom Pt at different adsorption positions on the BiOBr001-BiO surface (top, bridge and hollow site) are calculated by the first-principles calculation method based on density functional theory (DFT). More emphasis is placed on the research of the relative rule between single-atom Pt and BiOBr001 surface. The calculation results show that the BiOBr001-BiO system exhibits the appearance of surface energy levels and the shift towards the lower energy for valence band and conduction band, enhancing the photocatalytic oxidation performance, especially, the existence of surface energy levels below the conduction band will contribute to the separation and migration of electron-hole pairs and the significant improvement of photo-response capability. Besides, the work function of BiOBr001-BiO system is much lower than one of noble metal Pt, which is beneficial to the directional transfer of photogenerated charge. Therefore, the BiOBr001-BiO system should be selected as an ideal substrate for interaction with the noble metal Pt. Furthermore, single-atom Pt is adsorbed at different positions of BiOBr001-BiO surface, with induced impurity energy levels in the forbidden band, achieving the smallest adsorption energy, the best photo-response capability. Particularly, the transferred charge number is the largest value (–0.920e) when Pt atom is adsorbed on a hollow site. However, the open electron-poor region will be formed when Pt atom is adsorbed at the top and bridge sites of BiOBr001-BiO surface. What is more, our findings should provide the excellent theoretical guidance for achieving the photocatalytic CO₂ reduction and nitrogen fixation on the BiOBr001 surface to build up the top and bridge sites as the adsorption sites of Pt atom. The adsorption sites of Pt atoms are located at the hollow sites of BiOBr001 surface, which should obtain the high photocatalytic oxidizing activity of degrading organic pollutants. Finally, our work can not only present the basic data for the optimized local electronic structure and photocatalytic application for noble metal decorated BiOBr-based materials, but also provide a kind of research strategy for further exploring and designing efficient noble metal decorated BiOX-based or other semiconductor-based photocatalyst systems.