Abstract: The diffusion controlled ledge growth mechanism of bainite (DCLGMB) is reviewed briefly in this paper. It is argued that the existence of the ledge can not prove the existence of DCLGMB. A growth mode of lower bainite by shearing on the stacking fault face of austenite is proposed. In this mode, the thickening of lower bainite depends on the interfacial misfit dislocation loop (IMDL), which expands on the stacking fault faces of austenite. Ledges move only along the stacking fault faces but not along the side direction, and the side faces of ledges are not incoherent boundary. The observed experimental phenomenon of the austenitic stacking fault fringes corresponding to the lower bainitic growth ledges can be explained by the shear thickening mode.