An analytical vibration model was proposed to analyze a series of typical nonlinear behaviors of flexible rotor-system

such as resonance and oscillation coursed by couple interaction between linear and nonlinear forces during the speeding-up process. By introducing a nonlinear scaling factor ε

the model mainly probed into nonlinear response characteristics. Multi-scale method was applied to deduce the analytical pass-band solution of nonlinear rotor-vibration as a Fourier series form

and then obtain the nonlinear natural frequency and the fundamental-frequency frequency-response equation (FRE). A confirmatory experiment was made to verify the nonlinear characteristics of the analytical pass-band solution and the fundamental-frequency FRE under equal-scale condition (ε=1)

and also verify the rationality and effectiveness of the analytical couple-vibration model and the analytical pass-bomd solution.