The bifurcations of a rigid rotor-seal system were studied in a relatively wide parameter range.The transition boundaries of the system were obtained and the effect of the degree of rotor imbalance

clearance of the seal and the pressure drop of the flow in the seal on the bifurcations characteristics of the system was analyzed with fast Galerkin method in combination with Floquet theory.The result shows that the rotor system may undergo period doubling or Hopf bifurcations caused by the fluid-induced vibration.In some typical parameter ranges

the bifurcation diagrams of the rotor-seal system are acquired with numerical integral method.The simulation result verifies the correctness of the transition boundaries.The result provides the theoretical base for qualitatively controlling the stable operating state of rotors.