(1), taking ferrous sulfate as raw material, fully mixing with ammonia water in an ice bath, and then transferring to a stainless steel reaction kettle; (2) putting a stainless steel reaction kettle into a microwave heating device to react to generate a precursor of nano titanium dioxide; (3) centrifuging the precursor of nano titanium dioxide to obtain nano titanium dioxide, and washing the nano titanium dioxide with desalted water; (4) dispersing the washed nano titanium dioxide in an appropriate amount of anhydrous ethanol in an ultrasonic dispersion device; (5) slowly dropping diisopropylamine into the dispersion system, and filtering to obtain nano titanium dioxide. The invention has the advantages that the surface of nano titanium dioxide is treated with diisopropylamine, so that the dispersity of the powder is improved and the phenomenon of secondary agglomeration of nano titanium dioxide is solved; The average particle size of titanium dioxide is13-18 nm; The prepared nano titanium dioxide has good photocatalytic activity.