Abstract: The effect of phosphoric acid on the pH of metatitanic acid,the transformation of crude product into rutile,the achromatic force and the luminance of the samples was studied using the metatitanic acid hydrolyzed from titanium solution of ilmenite as raw material.The results show that the phosphate radical or hydrogen phosphate ionized from the phosphoric acid combines with the cations in the system to form precipitate,and the ionized hydrogen ions inhibit the ionization of metatitanic acid.With increase of the phosphoric acid content,the initial and terminal temperatures of the transformation of rutile crystals gradually increase.The content of P₂O₅ in the samples is positively correlated with the initial or terminal temperature of the transformation.In the potassium-phosphorus-aluminum salts treatment system,the achromatic force TCS and blue phase SCX of the samples decrease significantly at P₂O₅ content lower than 0.13%.When the P₂O₅ content is higher than 0.13%,the influence of phosphoric acid on TCS and SCX is not significant.Better brightness value of the crude product can be obtained at 0.15%~0.19% of P₂O₅ content.