Abstract: 45 steel eccentric axes cracked during different period of the machining process. By adopting metallographic examination,chemical compositions analysis and SEM fracture analysis,cracking reason for the eccentric axes was studied. The results show that cracking characteristic of the raw material turriform part,thermal refining eccentric axis and high frequency hardening eccentric axis were all the same. Many big size non-metallic inclusions in the raw material were the main reason for the cracking of the 45 steel eccentric axes.