<p>Full-face tunnel boring machines (TBMs) are subjected to intense impact loads and vibrations during excavation, which significantly affect their dynamic performance and service life. Based on the structural characteristics of multi-gear synchronous drive in TBMs, this study establishes a multi-degree-of-freedom nonlinear dynamic model of the main drive system. Multiple coupled factors such as time-varying mesh stiffness and nonlinear contact of the main bearing was incorporated. The input loads for the dynamic model are constructed by integrating the tri-directional loads of cutters and modifying the actual excavation loads. A stable segment of the cutterhead’s lateral and longitudinal vibration data was selected for comparative validation with the calculated response values from the dynamic model. Using real structural parameters as inputs, the dynamic characteristics of the system under different motor layouts and cutterhead rotational speeds are analyzed. The results show that, compared to the commonly used symmetrical layout in engineering, the X-type layout exhibits superior load distribution performance under strong impact loads. The maximum load difference is reduced by 37%. Furthermore, as the cutterhead rotational speed increases, the axial thrust slightly rises, while the total torque decreases significantly. The average tri-directional vibration displacement of the pinions decreases by approximately 20%–30%, and the system vibration period shortens noticeably. This study provides critical insights into the vibration characteristics and load distribution of TBM main drive systems. The effect of different design and excavation parameters was studied. This study provide theoretical and practical basis for ensuring safe and stable operation under complex working conditions.</p>