Al2O3, a common component in mold powder, is a kind of amphoteric oxide, which shows the characteristics of acid oxide under high alkalinity condition and shows the characteristics of alkaline oxide under low alkalinity condition. In this paper, the influence of Al2O3 on the flowing characteristics, melting characteristics and solidification characteristics of ultra-high basicity mold fluxes was analyzed. The results showed that with the increase of Al2O3, the viscosity and melting temperature increased, and the transition temperature decreased. In addition, the study also found that the initial crystallization temperature decreased by 34 ℃ on average when the Al2O3 content increased by 1 wt%. The average crystallization rate decreased with the addition of Al2O3 in the mold fluxes, and Al2O3 had a significant effect on the crystallization rate. The results showed that the proportion of crystals in the fracture decreased with the increase of Al2O3, but the crystal phase remained the cuspidine.