The invention discloses a Sr2FeTaO6 photocatalytic material as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) dissolving oleic acid into absolute ethyl alcohol, further adding sodium oleate, and performing sufficient stirring; (2) adding tantalum pentachloride to the solution, further adding an organic iron salt and organic strontiumsalt, and performing stirring to dissolve the components completely; (3) adding sodium hydroxide to adjust the pH value of the solution; and (4) adding the solution to a hydrothermal kettle, performing a hydrothermal reaction, after the reaction is completed, performing repeated rinsing by using absolute ethyl alcohol and water, and performing drying, so as to obtain Sr2FeTaO6 powder. Sr2FeTaO6 prepared by using an oleic acid-sodium oleate system is an environment-friendly iron-containing catalyst for photocatalytic degradation of nitrogen oxides in the atmosphere and has the advantages of being wide in reaction window temperature, high in catalytic activity, free of pollution, and the like, and the material is applied to denitration at room temperature and has a high conversion rate of NOx gases such as NO.