Abstract: Four multi-disk rotors with the same structure size are used as the research basis. The precision wire cutting method is used to prefabricate transverse cracks of different depths at different positions of the four rotors. The vibration characteristics of the cracked rotor system with changed crack parameters are tested and the relationship between the dynamic response characteristics of the cracked rotor and the crack location and crack depth is analyzed. The test results show that the 2× resonance phenomenon in the 1/2 critical speed zone and the 3× resonance phenomenon in the 1/3 critical speed zone are the typical characteristics of the ro? tating shaft crack failure. The 2× resonance peak value increases rapidly after the crack depth reached a critical point. While the 3× resonance peak value， which is different from the results of existing studies， drops abruptly after the crack depth reached a criti? cal point. Also， there is a correlation between the critical depth that triggered an abrupt change in the peak 2× and 3× resonance and whether the crack location is at the root of the disc.