This paper developed the kinematical model of squeezed film damper (SFD) stiffness rotor system based on the inertia parameter σ and bearing parameter B, then theoretically analyzed the amplitude-frequency characteristics and the transmission ratio characteristics of rotor system influenced with inertia parameter σ, bearing parameter B , and eccentricity ratio U. The analyzed results proved it could more clearly proclaim the vibration reduction mechanism of SFD when the film inertia force parameter σ was considered in the kinematical model of the rotor system. Moreover, the vibration reduction effectiveness of SFD not only limited by the unbalance of the rotor system, but also related with the selection of the bearing parameter B. In the research, it proved improper bearing parameter could directly influence the vibration reduction effectiveness of SFD, which founded theoretical basis for optical design of SFD.