The manufacturing method of titanium dioxide solution includes: mixing choline chloride, urea, boric acid, and titanium tetrachloride to form a first solution, wherein a molar concentration ratio of choline chloride to urea is 1:2, a molar concentration of titanium tetrachloride is 0.2 M to 0.4 M, and weight/volume of boric acid is 5 g/300 ml to 15 g/300 ml; and heating the first solute ion to form a second solution, wherein the second solution contains carbon/nitrogen doped titanium dioxide. In the manufacturing method of the present disclosure, the deep eutectic solution formed by choline chloride and urea may be used as a solvent, and may also be used as a carbon source and/or a nitrogen source. Therefore, titanium dioxide may be doped with carbon and/or nitrogen during the formation process.