Improved photocatalytic NO removal of photocatalysts requires enhanced carrier photocatalysis for more reactive species generation. Ultrathin structural BiOBr/BiOI (BiOBr/BiOI-U) photocatalyst was in-situ prepared and it showed enhanced photocatalytic efficiency for NO removal. The underlying photocatalytic process is divided into two steps: in the first step, NO3- was produced in a nonselective oxidation process. The increased NO3- concentration induces NO3- adsorption on the surface oxygen vacancies of the photocatalyst in the second step, which changed the surface environment of the ultrathin BiOBr/BiOI photocatalyst. During this process, the nonselective oxidation process turned into a selective oxidation process with NO2 as the main product. In addition, the main photogenerated reactive oxygen species contributed to NO removal. Furthermore, the photo catalytic mechanism of BiOBr/BiOI-U was explored.