The present invention belongs to a method for preparing organic ligand-capped titanium dioxide nanocrystals, wherein the method comprises steps of using methyl titanate, ethyl titanate, n-propyl titanate, iso-propyl titanate, butyl titanate or titanium tetrachloride as a titanium source, and with capping by oleic acid or an organic capping agent, reacting the titanium source in an organic non-polar solvent with an aqueous alkaline substance solution in the interface at a temperature of 25 to 280.degree. C. for 0.5 to 240 hrs, thus a transparent sol containing titanium dioxide nanocrystals is obtained, said the titanium dioxide nanocrystals have particle diameters of 1-20 nm. The preparing process has the features of mild reaction conditions and is a simpler and easier method with a shorter preparation period, thereby facilitating the industrialization.