Based on the predecessors of thermodynamic data, the relationship between aluminum contents and oxygen contents of the aluminum deoxidization reaction was calculated. And the influence of activity coefficient to the reaction equilibrium in bearing-steel is analyzed. First-order and second-order interaction coefficients were used to calculate and draw the equilibrium curves, respectively. The effects of different temperature and different interaction parameters on the deoxidization equilibrium curves were studied. And through the curve the influence of the change of aluminum contents to the activity can be known. The trend of the curve with first-order interaction parameters is consistent with the curve with first-order and second-order interaction parameters at the low Al concentration region. And the oxygen contents of curve with first-order interaction parameters are higher than the other curve at the high Al concentration region