Abstract: There are many cracks at the extended end of the rotating shaft during the service of the motor of a make-up hydrogen compressor.The causes of cracking and failure of the cracked shaft were analyzed by macro-morphology inspection, micro-examination, chemical composition analysis, mechanical property test and metallographic observation.The results show that there are machining tool marks in the fillet at the bottom of the shoulder, and the quenching and tempering process of the rotating shaft is improper, the metallographic structure after normal quenching and tempering is not obtained, the low strength and toughness of the rotating shaft material lead to fatigue, cracking and failure in the process of high-speed operation and alternating load, and the failure type is high-cycle fatigue.