A series of BiVO4 semiconductor photocatalysts with different crystallographic forms and crystallite sizes are designed and controllably constructed by a facile hydrothermal method, and their photocatalytic activities are examined for N2O decomposition. It is found that monoclinic BiVO4 prepared at 150 degrees C shows the highest activity because of its strongest adsorption ability for visible light and highest separation efficiency for photogenerated charge carriers, which achieves 26.7% N2O conversion at 25 degrees C after 12 h of irradiation. Oxygen vacancy significantly influences the photocatalytic performance of N2O decomposition, which can not only promote the formation of excess electrons but also reduce the activation energy barrier. Moreover, DFT+ U calculation is employed to explore the electronic properties of the catalyst at the microscopic level, as well as the reaction pathway of N2O decomposition over these photocatalysts, is illustrated.