Abstract: The nonlinear oscillator model for the dynamic characteristics of structures in flow,has been extended to studying nonlinear dynamic characteristics of rotor/seal system.It is emphasized that the rotor dynamic characteristics are ffected by the nonlinear unsteady flow in the small clearance.The numerical simulation and experimental results in a rotor/seal system of the centrifugal compressor are in a reasonable agreement.It is shown that the simulation provides a theoretical basis for predicting and preventing the occurrence of seal aerodynamic excitation and for investigating the mechanism of the seal aerodynamic excitation accident.