The effect of CaO-SiO2-CaF2 slag treatment on acid leaching of metallurgical-grade silicon was investigated in this study. Based on the analysis of the acid sensitivity of suicide precipitated phases, it was found that HCl + HF mixed acid was a better solvent to remove Si-Fe system intermetallics from metallurgical-grade silicon, and HCl was an effective leaching agent for eliminating Si-Ca system intermetallics from slag treated metallurgical-grade silicon. Acid leaching experimental results revealed that slag treatment enhanced the extraction of impurities Fe, Al, Mn, and Ti from metallurgical-grade silicon compared with results in the absence of slag treatment. Moreover, a remarkable decrease in the concentration of impurities B and P was attributed to the oxidation reaction in the slag refining process.