Boron (B) removal by slag refining using Na2O-SiO2 was investigated in industrial applications. The experimental results showed that the reasonable ratio range of slag to silicon is about 0.7-0.8; the suitable holding time is about 30min; the concentration of B is reduced from 1.90 ppmw to 0.17 ppmw by three times slag refining; and the removal efficiency of B reaches 91.1%. Moreover, it is discussed that B in silicon is more inclined to be oxidized by Na2O than SiO2 according to thermodynamic analysis and then volatilized to the atmosphere in the form of Na2B2O4 according to kinetic analysis.