A coupling rigid model for the generator stator and rotor was established. When the generator starts up in frequency conversion, there is high harmonic in electricity. In this condition, high harmonic magnetometive force was expressed and the component parts of electro-magnetic force were obtained. Then the effect of electro-magnetic stiff on the inherent frequency was analyzed. The nonlinear vibration of the vertical and horizontal coupling was studied, the first approximation solution and its corresponding steady-state solution were acquired, and the effect of electromagnetic damping and mass on resonance.