The invention relates to a preparation technology of a catalytic material, and aims to provide a method for preparing a porous manganese oxide catalyst. The method comprises the following steps: carrying out foaming treatment by using manganese salt, a hydrate of the manganese salt or an aqueous solution of the manganese salt as a precursor and a lipid polymer prepared from organic acid and alcohols in situ as a foaming agent, uniformly stirring after mixing the precursor, the organic acid, the alcohols used for carrying out esterification reaction with acid, the water and ethanol which is used as a solvent according to a mass ratio of 10 to 10 to 10 to 30 to 30, and heating and stirring under 50 to 170 DEG C until expanding and foaming; carrying out drying and roasting treatment on a thick colloidal-state matter obtained through foaming, thus obtaining the porous manganese oxide catalyst. The porous manganese oxide catalyst prepared by the invention has a porous structure and has excellent performance aiming at C-H bond activation reaction. Even under a solvent-free condition, the porous manganese oxide catalyst prepared by the invention is still capable of realizing efficient activated oxidation on ethylbenzene C-H bonds.