The invention relates to a method and system for preparing titanium dioxide. The method comprises the following steps: (1) by combusting dimethyl ether to supply heat, carrying out first preheating on titanium tetrachloride; (2) reacting aluminum powder and chlorine to generate aluminum trichloride to obtain a mixture containing aluminum trichloride and titanium tetrachloride, wherein the heat generated by the reaction between the aluminum powder and chlorine is used for carrying out second preheating on the titanium tetrachloride; (3) by combusting dimethyl ether to supply heat, carrying out first preheating on oxygen; (4) by combusting toluene to supply heat, carrying out second preheating on the oxygen subjected to first preheating; (5) mixing the mixture containing aluminum trichloride and titanium tetrachloride with the oxygen subjected to second preheating, and carrying out oxidation reaction on the titanium tetrachloride and oxygen to obtain an oxidation reaction mixture containing titanium dioxide and chlorine; and (6) carrying out gas-solid separation on the oxidation reaction mixture to respectively obtain titanium dioxide and chlorine. The method can be used for effectively preparing titanium dioxide.