B2O3 is employed as fluxing agent of high basicity CaO-based flux to substitute for CaF2. The effects of B2O3 and CaF2 on the metallurgy properties of CaO-based flux were investigated. The results indicate that the fluxing action of B2O3 is better than that of CaF2. For the high basicity CaO-based flux, when CaF2 is substituted with B2O3, the melting temperature can be decreased remarkably. Especially, when the mass ratios of CaO/SiO2 are in range of 5.25~8.0, the flux melting temperature is lower than 1300 °C. The inflection point temperature of flux viscosity-temperature curve is lowered remarkably when B2O3 is employed to substitute for CaF2. Meanwhile, the desulfurization capacity of flux can be improved markedly when CaF2 is substituted with equal mass of B2O3.