Abstract: The introduces the modified KRC and LFG models in association with a superelement model to calculate the equilibrium mole fraction of C at interphase interface, transforming force and temperature of phase equilibrium of γ&rarrα+ γ' and γ&rarrα+ cem transformations. The results show that there is no appreciable difference between the values obtained from the two activity models. The equilibrium mole fraction and phase equilibrium temperature will increase by adding such ferrite stabilizers as Si and Al, but decrease by adding such austenite stabilizers as Mn and Ni. The absolute value of transforming force and phase equilibrium temperature will increase after austenitic deformation.