Abstract: The bearing abnormal phenomenon appeared in service at 159 min. After disassembling inspection, a bearing steel ball was found to have cracked while the inner and outer rings no obvious abnormal. The failure mode and cause were analyzed by macro and micro observation, EDS analysis, metallographic examination and hardness testing. The results show that the cracking of the ball was fatigue cracking. The hole defects were residual hole, which formed in the electroslag melting process, and were not resected in subsequent processing. Casting hole was prolonged and flattened in the following process, which acted as the fatigue source during service. As a result, fatigue cracking took place.