Abstract: The microstructure of the white etching layer, especially for the deformed white etching layer, on high speed train flange was observed in this study. The white layers were thin and discontinuously distributed by making observation on a optical microscope. By using scanning electron microscopy, two types of microstructure were included in the deformed white etching layer, i.e. fine microstructure by plastic deformation and ferrite nanocrystalline by dynamic recrystallization.The amount of carbide in the white etching layer was related to the degree of plastic deformation and temperature rise, and the number and the grain size of carbide were low in the vicinity of surface. There are two mechanisms for the formation of the white etching layer. One was repeated plastic deformation mechanism, i.e. refinement of the ferrite grains and the dissolving the carbide. Another was deformation and temperature rise mechanism, i.e. formation of ultra-fine grain by dynamic recrystallization and dissolve of the carbide. The latter mechanism played a major role in refinement of grains.