Steel slagSteel slag contains Fe, Al, Si, and other valuable metals. It has complex mineral phase and large stock, resource utilization of steel slagSteel slag is urgent. In order to realize high value utilization of steel slagSteel slag, an idea of preparing Fe-Al-Si alloy from steel slagSteel slag in NaCl-KCl by molten salt electrolysisMolten salt electrolysis was proposed. The thermodynamicThermodynamics behavior of steel slagSteel slag in the process of molten salt electrolysisMolten salt electrolysis was analyzed theoretically. The results showed that molten saltMolten salt could not react with steel slagSteel slag in the absence of electricity. In the process of electrification, the reduction sequence of main elements in steel slagSteel slag was Fe, Si, and Al. Some by-products of potassium aluminate, sodium aluminate, sodium silicate, and potassium silicate were produced during electrolytic process. It was determined that the voltage range of the electrolytic process at 700–900 °C was − \(257\,\text{to}\,{-}3.37\,{\text{V}}\) . Under the above thermodynamicThermodynamics conditions, the alloy phases prepared by electrolysis of steel slagSteel slag were Fe3Si and Fe3SixAl1−x theoretically.