The invention relates to a preparation method of waterborne nano-antibacterial photocatalysis titanium oxide composite sol. The preparation method comprises the following steps: (1) carrying out acidhydrolysis; (2) purifying titaniferous solution; (3) carrying out peroxidation complexing on titanium; and (4) carrying out catalytic decomposition. According to the preparation method provided by theinvention, cheap titanic iron ore is adopted as a raw material, and orthotitanic acid is obtained without carrying out alkali precipitation on titanyl sulfate. The preparation method has the advantages that zinc peroxide is taken as a reactive substance, peroxyl and titanium ions directly form a complex and are dissolved into water, secondary purification dissolution does not need to be carried out, and zinc sulfate formed by Zn ions and sulfate radicals has antibacterial and deodorizing effects, so that steps are simple and convenient; meanwhile, Fe<2+> is introduced as a Fenton catalyst, sothat titanium peroxide is rapidly decomposed and generates titanium oxide, gelatinization of the titanium peroxide is avoided, and the titanium oxide and zinc sulfate form a composite antibacterial product. The prepared composite product is uniform in particle morphology, use of alkaline and discharge of wastewater can be greatly saved, and the preparation method provided by the invention is simple in technology and is applicable to large-scale industrial production.