Abstract: This paper studies aluminum leaching by sulfate acid from Al-Ca residue. The optimum conditions of leaching are obtained. The optimal conditions are adjusted by 3 stages counter -current extracting to improve extracting yield. The aluminum sulfate solution produced meet the requirements of the following operation. The optimal extracting yield reaches 98.48 %. The pH value of aluminum sulfate solution is controlled at 3.5. The concentration of aluminum sulfate 163.4 g/L.