The invention discloses a method for preparing a hydrophobic Cr-Mn-base catalyst by ultrasonic-hydrogen reduction, which comprises the following steps: dissolving chromic nitrate and manganese acetate in deionized water to prepare a chromic nitrate/manganese acetate mixed solution; adding Al2O3 particles into the mixed solution, oscillating at constant temperature while ultrasonic immersing, drying and roasting to obtain solid particles; carrying out reduction treatment on the solid particles in hydrogen, and roasting in air to obtain the hydrophobic Cr-Mn-base catalyst. The catalyst preparedby the method disclosed by the invention is mainly used for catalytically combusting chloric volatile organic compounds; transition metals are substituted for noble metals, thereby lowering the cost on the premise of maintaining the high activity of the catalyst; and thus, the combustion of the chloric volatile organic compounds can be catalyzed at lower temperature. The catalyst still has high activity at high outside humidity, and thus, having wide prospects in practical application.