The nonlinear dynamic model of the underwater turbine rotor has been established considering the radial internal clearance of the bearing, the nonlinear Hertz contact force and the unbalance of the rotor. The numerical analysis of the dynamic model has been performed by using Rouge Kutta Felhberg of variational step and the nonlinear dynamic characteristics of the system have been analyzed based on the bifurcation and chaos theory. The results indicated that the chaos of the system broadened with the enlargement of bearing clearance; with the increase of the rotating speed, the system would pass through period, quasi period and chaos processes under the excitation of the unbalanced and the nonlinear Hertzian contact force.