Abstract: In order to remove calcium sulfate in metatitanic acid produced by sulfate process,the changes in solubility of calcium sulfate in solutions containing 1% sulfate acid with addition of different cosolvents were investigated by isothermal equilibrium method,and then the removal of calcium for metatitanic acid was carried out using the better cosolvents under optimum conditions. The results show that the sequence of dissolving-aiding effect is ammonium citrate > sodium chloride > mixture of magnesium chloride and sodium chloride > magnesium chloride,and the optimum conditions for ammonium citrate and sodium chloride are 55 ℃ of temperature,10% of mass concentration and 0.5 h of dissolution time,respectively with 7.63 g/L and 9.84 g/L of solubility for calcium sulfate. Sodium chloride has a better efficiency for calcium removal than ammonium citrate and does not affect the quality of final product. The research has important realistic meanings for decreasing the calcium content in titanium dioxide and improving the quality of final product.