Abstract: In order to eliminate the hazard effects of the leaching of fluorine in mold fluxes,this paper introduces a mold flux with high Al₂O₃ content. The effects of Al₂O₃ content on the concentration of F^- ions and the pH value of leaching water were investigated,and the dependence of Al₂O₃ on the structure of mold fluxes was analyzed by X-ray photoelectron spectroscopy(XPS). When the mass fraction of Al₂O₃ is 4%,the concentration of F^- ions in leaching water is about 22.8 to 35.4 mg·L^-1,and the pH range is between 4.0 and 9.5. The F^- concentration and the pH range initially reduces and then slightly rises again as the Al₂O₃ content increases from 4% to 34%. The XPS spectra show that the Al-F bond forms in the mold flux when the Al₂O₃ content increases. This can restrain the dissolution of fluorine in water. Controlling the content of Al₂O₃ between 16% and 34%,the F^- concentration in leaching water is about 4.0 to 10.0 mg·L^-1,and the pH range is between 6.5 and 7.5. This is helpful to reduce the hazard effects of the leaching of fluorine in mold fluxes.