Abstract: Based on phase equilibrium and thermodynamics, the oxygen transfer mechanism from refractory to molten steel and relevant influencing factors were studied. The results showed that the equilibrium partial pressure of O2 in closed pores due to decomposition of oxides in the refractory is much higher than that in molten steel which has been deoxidated to a high degree. The fact reveals what are the main influencing factors on the oxygen transfer from refractory to molten steel. In addition, according to what kind of the refractory used and its composition, the ability to transfer oxygen will be different from other refractories. The lower the oxygen content in molten steel, the more the oxygen transferring from refractory to molten steel and the components of decomposed.