The dynamic model of the marine rotor-bearing system is developed on the short bearing theory after considering the yawing motion， which shows that the differential equations are of strong geometric nonlinearity. Due to the influence of yawing motion， the rotor will deflect relative to the bearing bush and be subjected to various forces such as nonlinear oil film moment. The nonlinear dynamic characteristics of the rotor system under yawing motion and the deflection motion are analyzed by numerical method. The influence of yawing amplitude and frequency ratio on the rotor motion is also studied. The results show that the rotor amplitude and deflection relative to the bearing bush are large at low speeds. And at high ones， the yawing motion causes the rotor to produce the chaotic oscillation. The amplitude of rotor and its deflection increase with the amplitude of yawing. With the decrease of the frequency ratio， the influence of yawing on the rotor gradually weakens.