There are two types of mechanisms for illustration of bainite transformation: diffusional and displacive. Modeling studies on various kinetic equations based on diffusional growth mechanism were conducted. A reasonable modification about diffusional kinetic models is achieved. It is found that the growth rates of bainitic ferrite could be simulated by the kinetics of carbon volume diffusion in some steels, but in heavily alloyed steels a large discrepancy is found. These indicate that the kinetic model based on diffusional mechanism is only valid for some steels but not all. Coupled with the effect of substitutional atoms, bainite transformation mechanism is discussed.