The invention discloses a preparation method of a modified active carbon fiber with surface-loaded nanometer titanium dioxide (TiO2), and belongs to the field of photo-catalytic materials in environment protection. The preparation method has broad study and application prospect in the fields of water purification, wastewater treatment, waste gas treatment, air purification, disinfection and sterilization, and the like. The preparation method comprises the following steps of putting the modified active carbon fiber into a mixing solution of nanometer TiO2 (Degussa P25), acetone, epoxy resin, UV-P and nanometer Fe2O3 (ferric oxide), fully impregnating, and drying under the nitrogen atmosphere, so as to obtain the modified active carbon fiber with surface-loaded nanometer titanium dioxide. The preparation method has the advantages that the obtaining of the used raw materials is easy, the preparation method is simple, the adhesion degree of the nanometer TiO2 layer is high, the stability is good, the load is uniform, the wavelength range of exciting light is broad, the photo-catalytic property is good, and the like; the preparation method can be widely applied to the fields of water purification, wastewater treatment, waste gas treatment, air purification, disinfection and sterilization, and the like.