The invention relates to a preparing method of nano titanium dioxide. The preparing method is characterized by comprising the steps that white suspension is obtained after an alcohol-thermal reactionis carried out with titanyl sulfate as a titanium source and absolute ethyl alcohol as a solvent; the suspension is filtered, washed clearly with absolute ethyl alcohol, and dried and calcined to obtain nanoparticle-type titanium dioxide. The preparing method of nanoparticle-type titanium dioxide is simple in reaction condition, nanoparticle-type titanium dioxide can be obtained simply by mixing two raw materials and carrying out a reaction for a certain period of time at proper temperature and pressure, and the preparation can be completed without adjustment of the pH value.