Bi/BiOBr composites with oxygen vacancies were synthesized by a simple combustion method. The as-synthesized catalysts were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, UV-Vis diffuse reflectance spectroscopy, and photoluminescence spectroscopy. Along with the formation of BiOBr, the reduction of partial Bi3+ cations was achieved, and thus Bi/BiOBr composites were one-pot obtained. Moreover, the formation of oxygen vacancies was confirmed. Compared with pure BiOBr, Bi/BiOBr composites exhibit significantly improved photodegradation performances under visible light irradiation, which can be attributed to the surface plasma resonance effect, electron sink effect of metallic Bi nanoparticles, and the narrowed band gap caused by the formed oxygen vacancies. Moreover, the main active species and photocatalytic mechanism of Bi/ BiOBr under visible light irradiation were discussed in detail.