The invention relates to a method for preparing a carbon nanotube-supported metal nanoparticle catalyst by using a photochemistry method to reduce MnPd and belongs to the field of catalyst preparation technologies. The method comprises the following steps of respectively soaking a carbon nanotube into acetone and NaOH solution, stirring by NH4F solution, and naturally cooling to the room temperature after vacuum drying to obtain a carbon nanotube after modified treatment; and reducing a metal nano-colloid by using the photochemistry method; carrying out ultrasonic treatment on the obtained carbon nanotube after modified treatment and the obtained metal nano-colloid, continuously stirring for 3-6 hours, cleaning through distilled water, carrying out vacuum filtration and drying to obtain the supported metal nanoparticle catalyst. The method utilizes the same reduction system (acetone-PEG-ultraviolet radiation) during reduction of Mn and Pd; the process is simple, green and environmental-friendly; the nanometer manganese oxide prepared by the method has a smaller and uniform size, and the surface has a large amount of defects, which is beneficial for interaction with the Pd in a catalytic process to carry out catalytic oxidation on methanol.