Abstract: Boron removal is one of the most important steps for metallurgical method in preparing solar grade silicon.The thermodynamic behavior of impurities in metallurgical grade silicon was studied using O₂ gas blowing.The order of difficulties for impurities removal was confirmed through the standard Gibbs free energy of formation.The relationships between the boron content in silicon and the equilibrium partial pressure of gaseous boron species were obtained through the thermodynamic calculation. Results show that it is the most for the volatility of BO and the equilibrium partial pressure for BO is reduced from 2.5 Pa to 0.05 Pa at 1 750 ℃ when the boron content in silicon decreases from 5 × 10^-6 to 0.1 × 10^-6.It was presumed that the gaseous species BO is the main form for boron volatility from metallurgical grade silicon melt and it is helpful for boron removal with higher refining temperature using O₂ blowing.