Abstract: The SKH51 high-speed steel shaft sleeve cracked during the nitriding process. The causes of shaft sleeve cracking were analyzed using methods such as macroscopic observation, chemical composition analysis, hardness testing, metallographic examination and scanning electron microscopy analysis. The results show that the distribution of eutectic carbides in the shaft sleeve matrix was uneven, and there were severe strip-shaped eutectic carbides along the axial direction. Insufficient tempering of the material results in the presence of residual austenite in the structure. During the nitriding process, the residual austenite transformed into martensite, resulting in structural stress. The chamfer radius at the crack location of the shaft sleeve was too small, resulting in stress concentration and ultimately led to the cracking of the shaft sleeve.