An unbalanced rotor dynamics model supported on ball bearing was established. In the model of ball bearing, three nonlinear factors were considered, such as the clearance of bearing, nonlinear Hertzian contract force between balls and races, and the varying compliance vibration because of periodical variety of contact position between balls and races.In the model of rotor, rotor’s unbalance force, which varies with rotating speed, was considered. The numerical integral method was used to obtain nonlinear dynamic responses, the effects of rotating speed and the bearing clearance on dynamic responses were analyzed, and the bifurcation plot, phase plane plot, frequency spectrum and Poincaré map were used to carry out the analysis of bifurcation and chaos motion. Period doubling, quasi-period loop breaking and mechanism of intermittency had been observed as the routes to chaos.
