Squeeze film damper (SFD) - dual rotor system, widely used in aero engines, is investigated in this paper. A dynamical model about SFD - dual rotor system with spring support is set up, in which not only the forces between the high - pressure rotor and low - pressure rotor but also the nonlinear oil - film forces are considered. The model is solved by 7 - 8 order continuous Runge - Kutta method. The characteristics of nonlinear vibration and the forces between the rotors are got. These are useful in vibration monitor and fault diagnosis for aero engines.