The invention belongs to the technical field of functional materials, and relates to a preparation method of a titanium dioxide/silver composite nanomaterial. The method comprises the following steps: dissolving and uniformly mixing titanium acetylacetonate and silver nitrate in an alcohol solution, carrying out a combustion reaction at a certain temperature, and carrying out heat treatment in a muffle furnace to obtain the titanium dioxide/silver composite nanomaterial. The preparation method is simple and easy, and the titanium dioxide/silver composite nanomaterial has the advantages of high purity, low content of impurities, low preparation cost, excellent performances, and realization of industrial batch production. The titanium dioxide/silver composite nanomaterial prepared in the invention has high catalysis activity as a photocatalytic material, and has wide application prospects in the field of degradation of dye wastewater and indoor harmful gases and the field of photocatalytic disinfection.