Abstract: Considering the time-varying instantaneous center, meshing stiffness and static transmission error, a dimensionless dynamic model of the gear was established based on elastic rotational angle separation method. A multi-term harmonic balance method (HBM) was applied to obtain the approximate analytic solution of the gear under compound excitations composed of the instantaneous center and meshing stiffness. The effects of the system parameters on the dynamic response and the sensitivity of the parameters were analyzed emphatically. Results show that there exist multi-frequency harmonic components in the gear dynamic responses; the vibrational amplitudes grow with different tendencies as the rotational speed, the eccentricity, the error, the amplitude ratio of the meshing stiffness and the load torque increase; and every parameter of the gear has a greater influence on the sensitivity of itself and others.