Some numerical models such as central atoms model (CAM) and superelement model were used to simulate the thermodynamics of austenite decomposition in the Fe-C-Mn-Si TRIP (transformation induced plasticity) steels. Thermodynamic calculations were carried out under a para-equilibrium (PE) condition. The results show that certain silicon content can accelerate the polygonal ferritic transformation and increase the volume fraction and stability of retained austenite by retarding the precipitation of carbides during the bainitic transformation.