Abstract: Generator retaining rings operate under the condition of high speed and stress. Due to the different hardness of generator journal and generator retaining rings as well as permanent deformation caused by frequent disassembling, the pre-tightened stress of the originally close-connected structure between generator journal and generator retaining ring is reduced dramatically. The reduction will lead to the looseness of connection. Moreover, the looseness makes it easy to produce fatigue cracks. The cracks are difficult to detect because the echoes by them are in the almost same position with the echoes by the joint surface. This article adopts the double-crystal transceiver probe detection method to collect the dynamic echoes of cracks produced at both ends of the generator retaining rings. The method has detected the dynamic echoes of the 0.5 mm Linear cutting groove and two cracks on the No.3 generator retaining ring in a factory province, which has proved the feasibility of the method.