Abstract: To investigate the influence of root cracks on the load-sharing characteristics of herringbone planetary gear system, a 23-degree-of-freedom bending-torsional-axial coupled dynamic model was established, considering the effects of crack length, mesh stiffness, and damping. The time-varying mesh stiffness (TVMS) of the cracked system was derived using the potential energy method, and the system’s nonlinear dynamic equations were solved by the Runge-Kutta method to obtain the dynamic meshing force and load-sharing coefficient. The results indicate that the presence of gear cracks reduces the system’s TVMS and induces obvious excitations in the load-sharing curve. As the crack propagates, the load-sharing coefficient first decreases and then increases, showing a gradual deterioration of the load-sharing performance. Under constant manufacturing errors, the load-sharing coefficient of both internal and external meshing pairs increases with crack severity, indicating degraded load-sharing capability. Conversely, when the crack size remains unchanged, increasing manufacturing errors also cause the load-sharing coefficient to rise, further confirming that the load-sharing performance deteriorates with larger errors.