Abstract: In order to clarify the impact mechanisms of B₂O₃ on the stability of high aluminum and low magnesium slag, based on the actual composition of blast furnace slag in the field, the viscosity and microstructure of slag were investigated by the high-temperature melt properties tester, Factsage software and XPS spectroscopy. The results showed that slag viscosity decreases with the increase of B₂O₃ content and the stability of slag increases with the increase of B₂O₃ when the slag temperature is lower than 1360℃.The slag stability is the best when the slag temperature is 1216℃ and the content of B₂O₃ is 2.0%.The liquid region of slag gradually expands to the MgO region with the increase of B₂O₃ content, The addition of B₂O₃ not only improves the refractory phenomenon of slag caused by excessive MgO content, but also improves the stability of slag when the binary alkalinity fluctuates.