The invention discloses a method for preparing nano-TiO2 serving as a cathode material of a lithium ion battery. The method comprises the following steps of: beating precipitates of titanium prepared from metatitanic acid or various titanium sources by using water, adding a coordinating agent into thick liquid according to a molar ratio of the coordinating agent to the titanium of 1.0:1-10:1, regulating the pH value to be between 7 and 14 by using alkali, reacting in a stirring reactor at the temperature of between 20 and 80 DEG C for 10 to 720 minutes, and filtering to obtain solution of thetitanium; and adding the alkali into the solution according to a molar ratio of the alkali to the titanium of 1.0:1-50:1, heating the solution to between 80 and 200 DEG C for 10 to 600 minutes, filtering and washing to obtain a precursor of nano-TiO2, and calcining the precursor at the temperature of 120 and 850 DEG C for 0.5 to 20 hours to obtain the nano-TiO2 serving as the cathode material of the lithium ion battery. The method has the characteristics of wide range of raw materials, simple process flow, low energy consumption, low cost, good appearance of product granularity and excellent electrochemical properties.