Abstract: To reduce the insolvable solid-phase object emerged during acidolysis of sulfate process route for titanium pigment production,the structures and compositions of the object are analyzed. It can be concluded through laboratory experiments that insufficient mixing of sulfuric acid and ilmenite concentrates and incomplete acidolysis reaction are main reasons for forming the solid-phase object which is difficult to be leached during acidolysis. Through taking the premixing process for acidolysis in a certain titanium pigment plant as an example,the factors that affect the premixing effects are further analyzed and solutions are proposed. By adjusting the preparation of sulfuric acid and reducing the temperature of sulfuric acid,the problems including low leaching rate and large volume of residual solid-phase object are completely solved with the leaching rate reaching 96% and the volume of solid-phase object on the wall of acidolysis pot reducing from 30 m³ to less than 3 m³.