Abstract: For a coaxial Face Gear Split-Power transmission system, the influence of gear manufacturing errors on the dynamic load-sharing characteristics of the power splitting and converging stages is investigated. A lumped-parameter method is employed to establish a bending-torsional coupled dynamic model with 45 degrees of freedom, comprehensively incorporating manufacturing errors, time-varying meshing stiffness, and damping. The relative displacement expressions for each meshing pair are derived and dimensionless processing is performed. The system dynamic equations are solved using the Runge-Kutta method, and a dynamic load-sharing coefficient is introduced to quantitatively evaluate the load balance among branches. Simulation validation is carried out using a rigid-flexible coupled model in Adams. The results show that a 5 μm manufacturing error in the first stage drastically expands the fluctuation range of its load-sharing coefficient from 0.967–1.068 to 0.008–2.747, with the fluctuation amplitude increasing by more than 25 times. The error disturbance attenuates significantly when transmitted backward; the load-sharing coefficient fluctuation in the third stage is only 0.950–1.048, corresponding to an attenuation rate of over 90%. As the manufacturing error increases from 2 μm to 20 μm, the mean load-sharing coefficient of the first stage rises from 1.33 to 2.40, indicating continuous deterioration of the system’s load-sharing performance. This study quantitatively reveals for the first time the stage-by-stage attenuation law of manufacturing errors in a coaxial face-gear split-and-confluence transmission system, providing a reference for system tolerance allocation and load-sharing optimization.