Abstract: As one important part of the giant wheel, the main spindle is difficult to be disassembled. While failure occurred on the main spindle, the risk is rather high. According to the structure characteristics of the main spindle on giant wheel, the method of AE testing was established, and the abnormal sound, which was produced by the main spindle, was detected on-line in this paper. The author acquired the AE characteristics of the abnormal sound, including AE location features, parameter distribution features and wave spectrum characteristics. Also, the twice results of AE testing in two test cycle were compared in the paper. The results indicated that the AE technique could be applied to the state monitoring and evaluation of the main spindle on giant wheel.