A concentric face gear torque split system used in the helicopter main transmission to transfer more power and reduce the structure weight is introduced. A mathematical model is proposed to analyze the vibration characteristics as well as load sharing performances of the torque split system. The excitations including mesh stiffness, backlash, static transmission error, and system work torque are considered in the model. The vibration property, dynamic displacement responses, and the system factors which affect the load sharing capacity of the system are studied based on the numerical analysis results. The results show that vibration forms of the system can be classified into three categories: pinion vibration mode, face gear vibration mode, and pinion coupled face gear mode. Resonance peaks and jump phenomena are detected around rotation speed 5772 rpm and 10,250 rpm, mainly related to the coupled translational–rotational–axial of face gears vibration modes. In addition, appropriate gear pair backlash and pinion distribution angle parameters are significant to improve the dynamic load sharing capacity. The increase of the pinion bearings' supporting stiffness will generate worse load sharing characteristics and a relative flexible bearing is recommended to the pinions' supporting.