The invention relates to a method for preparing perfluoro-isopropyl ethyl ketone. The method comprises the step: with perfluoropropylene and oxygen as raw materials and fluoride salt as a catalyst, under the ultraviolet irradiation condition, reacting to obtain perfluoro-isopropyl ethyl ketone. According to the method provided by the invention, a product can be obtained by a one-step reaction, sothat the method is simple, convenient and practicable; and the method is easily available in raw materials, low in cost, few in side reaction and mild in reaction condition, so that the method is beneficial for large-scale industrial production.