Abstract: The experimental study was conducted on the stability of rotor-sliding bearing systems by the transient perturbation．The test results show that in some speed range, even larger range, of approaching the system threshold of stability, the transient perturbation with the certain strength will result in the OLL WHIRL of the system，and after that limit the system does not necessarily diverge but often converges to a limit cycle and does the so called half-frequency" whirl．At the same time the test results show that the magnitude of the half frequency whirl is generally larger than that of the same frequency whirl, and the value of the former frequency depends mainly on the operation speed，not the threshold of the system stability with no outside disturbence．

Key words: Experimental study, Limit cycle, Rotor-bearing system, Stability, Transient perturbation