Graphitization process is the formation process of graphite particles in graphitized steel, which is the key process to control the microstructure and properties of the steel, it is of great significance to study it. Therefore, in this paper, the quenched high carbon steel with 0.66% carbon was graphitized at 650 ℃, 680 ℃ and 710 ℃ respectively. The microstructure of the graphitization process was analyzed by field emission scanning electron microscope FESEM, electron probe microanalysis EPMA, X-ray diffraction XRD and transmission electron microscope TEM, and according to the dynamic theory of phase transformation the kinetic curve of graphitization process was drawn and the corresponding kinetic equation was established. The results show that in the process of graphitization, the quenched martensite first transforms to the stable state of precipitation carbide, and when the carbide is cementite Fe3C, the precipitation rate of graphite particles begins to increase significantly. The acicular α -Fe in the matrix recrystallizes, and the acicular α -Fe is gradually replaced by equiaxed ferrite; the content of C in ferrite decreases gradually with the prolongation of graphitization time, that is, it changes from supersaturated state to stable state. The content of C increases to the peak value in graphite particles, while that of Fe and Si decreases to the valley value, this shows that, the decomposed carbon of cementite Fe3C diffuses to the graphite core, while Fe, Si diffuse from the graphite core, then graphite particles are formed. The dynamic process of graphitization of tested steel accords with the JMAK equation, and the value of n in the equation is between 1.5 and 1.7. According to this, it can be inferred that the nucleation rate of graphitization decreases with time.