Abstract: A bear ing-rotor system is analyzed by using a new analytic model of the unsteady oil film force. The bifurcation and chaos behavior of the rotor system varying with the r otation angular fr equency are obtained through numerical simulations. Using the shooting method of nonlinear dynamic analysis, the periodic solutions of the systemare obtained, and unstable forms of differ ent periodic or bits are judged by the leading Floquet multiplier. Doublingbifurcation, second Hopf bifurcation and saddle-node bifurcation are found, and an adding three2period bifurcation isobserved by using t he shooting method and Runge-Kutta method.

Key words: rotor system, shooting method, Floquet theory, stability, bifurcation