Overhaul slag is a hazardous waste which is from the process of aluminum electrolysis industry. In this work, a technology of calcium sulfate roasting and water leaching was developed to dispose of overhaul slag. The effects of roasting and leaching parameters were investigated in detail. Under the optimal roasting conditions, the fluorine could be stably solidified into CaF2, and lithium could be converted into soluble NaLi(SO4). The roasted clinker was then subjected to water leaching for the selective extraction of lithium. About 99.74 % of lithium was extracted and 99.82 % of fluoride was solidified by the leaching process under the optimal leaching conditions. After water leaching, the concentration of lithium can reach 2.3 g/L. XRD analysis shows that the main phases of the aqueous solution after evaporation and crystallization are NaLi(SO4) and Na2SO4, and a small amount of impurities can be further removed and concentrated to prepare Li2CO3. The main components of leaching slag are C, Al2O3 and CaF2, which can be used as fast setting cement. The process proposed in this paper is not limited to the recovery of high-value lithium from overhaul slag, and can be applied to the extraction of other valuable waste substances in aluminum industry.