Bismuth oxychloride micro-sheets with rich oxygen vacancies (BiOCl-OV) are firstly prepared through a surfactant assisted solvothermal method. Due to the selective surfactant adsorption, the as-prepared BiOCl-OV exposes high percentage {0 0 1} facets. Moreover, the ion-exchange process not only introduces Br atoms but also creates cavities in crystal structure of the Br doped BiOCl-OV (Br-BiOCl-OV). When used as photocatalyst for N photo-fixation, the optimized Br-BiOCl-OV demonstrates an ammonia producing rate of 6.3 μmol h under visible light irradiation, which is greatly enhanced than that of pristine BiOCl-OV (4.1 μmol h). The density functional theory (DFT) calculation suggests that because of the introduced Br atoms and the oxygen vacancies, the adsorbed N on Br-BiOCl-OV exhibits greater NN bond length than that adsorbed on pristine BiOCl-OV, attributing to the effective activation of the inert NN bonds. Photocurrent response, state/transient PL spectra and electrochemical impedance spectroscopy indicate that the Br-BiOCl-OV possesses promoted charge separation and suppressed charge recombination, which finally leads to the high N photo-fixation performances.