Abstract: Preparation of TiO₂ with titanium slag by molten-salt method is a new way to produce TiO₂ in which the preparation of metatitanic acid by hydrolysis is an important step due to its huge influence on the quality and yield of the finished products.This paper has identified the factors including concentration of titanium solution,F value and hydrolysis time that influence the grain size and conversion ratio of the metatitanic acid.The results show that the hydrolysis ratio of the titanium solution under different temperatures remains relatively low during the initial 30 min,and after 50 min it rises quickly while after 100 min,the variation of the hydrolysis ratio with time becomes milder.With the increase of temperature,the F value becomes lower,and with the decrease of the concentration of titanium solution,hydrolysis reaction proceeds faster and a higher ultimate conversion ratio can be obtained as a result.At the beginning,the grain size of the metatitanic acid resulting from hydrolysis increases with the time of the hydrolysis reaction.Three hours later,the grain size of the metatitanic acid exhibits a little fluctuation with time.The grain diameter of the metatitanic acid decreases with the increase of the concentration of titanium solution and F value and increases with better stability of the titanium solution.During preparation of metatitanic acid in the new TiO₂ pigment production process,the TiO₂ concentration and F value should be controlled at about 200 g/L and 1.8 ～ 1.9 respectively,and hydrolysis process should be carried out for 4 hours under the condition of slight boiling.