The invention provides a method for preparing nano-TiO2. The method comprises the following steps: contacting a titanium source and a water-soluble alkaline substance in the presence of an aqueous solvent under a hydrolysis condition, wherein the titanium source is a titanium compound having the following structure [TiClx(OR)(4-x)][R'OH]y, x is 1, 2 or 3, y is 0, 1, 2, 3, 4 or 5, and R and R' are same or different alkyls. According to the method, hydrolysis can be carried out at a relatively low temperature. Compared with methods in the prior art of using titanium tetrachloride or titanium tetraol as a titanium source, the method has the advantages of greatly reducing water consumption and effectively reducing wastewater drainage.