The invention relates to a method for preparing a photocatalyst for treating petroleum pollutants in water. The method is characterized in that titanium dioxide and Cu and Mn oxides are taken as active ingredients and are loaded on a floating type foaming ceramic carrier through adopting a rolling load technology. The method comprises the following specific steps: (a) dissolving titanyl sulfate into deionized water, regulating the pH value to 7-10 by using a 5-25% ammonia solution, cleaning the obtained white precipitate centrifugally, mixing the white precipitate with the deionized water, pulping and regulating the pH value to 7-10 under a mixing condition by using H2O2 and HCl so as to obtain titanium sol; (b) dissolving manganese salt and copper salt into the deionized water, mixing with a permanganate solution, dripping a NaOH solution to regulate the pH value to 8-12 and spray-drying the obtained size to obtain catalyst precursor powder; and (c) adding foaming ceramic balls into a rotary granulator, spreading the catalyst precursor slowing under the rolling condition, spraying titanium sol to be used as an adhesion agent, carrying out roll coating, drying and calcinating to obtain a catalyst finished product.