<p>For the accessory gearbox of aero-engines, the gear transmission system is increasingly pursuing a lightweight design, which leads to flexible vibration of gears. However, the most popular lumped-mass modeling approach cannot capture the flexible vibration of gears, whereas solid element models result in extremely low computational efficiency. Therefore, this paper aims to develop a reduced dynamic model of a gear system to balance the computational accuracy and efficiency. First, the meshing stiffness of the gear pair is calculated based on the loaded tooth contact analysis method, and the meshing element between the driving and driven gears is established. Then, a dynamic model of the gear transmission system is proposed based on the solid elements, and the degrees of freedom of the dynamic model are reduced using the Guyan method. Finally, the reduced dynamic model proposed in this paper is verified through comparison of modal characteristics and dynamic responses on the basis of ANSYS and ADAMS. The results demonstrate that compared with other existing modeling approaches, the proposed dynamic modeling method achieves a favorable balance between computational accuracy and efficiency. Additionally, the tooth flexibility has negligible influence on the low-order modes of the system and the amplitude of the meshing frequencies. This study can provide an effective methodology for establishing dynamic models, offering valuable guidance for subsequent investigations into vibration mechanisms.</p>