La₂O₃–SiO₂–Al₂O₃ was selected as the basic slag system, a hemispherical method was used to study the melting temperature of specified areas. The results showed that, for different La₂O₃ mass contents (45%, 50% and 55%) in the La₂O₃–SiO₂–Al₂O₃ slag, the melting temperature was the lowest when the SiO₂/Al₂O₃ mass ratio was about 2. A small amount of the minor component, FeO, B₂O₃ and MnO could lower the La₂O₃–SiO₂–Al₂O₃-based slag melting temperature, the effect of B₂O₃ was particularly significant. The addition of a small amount of FeO and B₂O₃ has an additive effect on decreasing the slag melting temperature. The melting temperatures of slags 65%La₂O₃–16%SiO₂–8%Al₂O₃–7%FeO–4%B₂O₃ and 65%La₂O₃–19.3%SiO₂–9.7%Al₂O₃–2%FeO–4%B₂O₃ were 1319 and 1386℃, respectively.