The invention provides a preparation method of benzophenone. Diphenylmethane is used as a raw material, and in the presence of a catalyst, an oxidant H2O2 is added to perform the oxidation so as to prepare the diphenylketone. The preparation method has the advantages of environment-friendly oxidant, moderate reaction condition, simple and convenient operation, no heavy metal or transitional metalions, less side reaction, high reaction yield, high safety, low requirement on equipment, easy operation, suitability for industrialized production and the like.