Abstract: In order to meet the requirements of the processing technology, the bearing ring forging blank was subjected to spheroidizing annealing treatment. The microstructure of the surface layer of bearing ring forging blank after spheroidizing annealing was analyzed. The results show that the decarburization layer would be formed on the surface of forging blank if the carbon potential of furnace gas was not properly controlled. As the furnace carbon potential gas gradually decreased, corresponding to the formation of different spheroidized structures, the corresponding relationship between the two conforms to the error solution of the Fick equation of the diffusion law. Combined with the Fe-Cr-C ternary phase diagram, different furnace gas carbon potential would lead to different carbon content. A carbon concentration curve was drawn and the transformation of the surface structure conformed to the change rule of the curve.