The invention relates to a preparation method of a palladium-platinum bimetallic catalyst. The preparation method is characterized by using active carbon as a carrier, pretreating the active carbon respectively by hydrochloric acid and nitric acid before preparation, then simultaneously loading palladium and platinum on the pretreated active carbon, and adding an activating agent into the active carbon with palladium and platinum for reduction to finally obtain the palladium-platinum bimetallic catalyst. According to the invention, the preparation method is simple; and the obtained palladium-platinum bimetallic catalyst disclosed herein has the advantages of high activity, long life, etc, and is especially suitable for preparing o-phenylenediamine by solvent-free hydrogenation.