In the split-torque drivetrain, thin-walled herringbone gears are advantageous for their high power density. However, investigating the vibration characteristics of these gears poses a persistent challenge due to the inherent flexibility of the gear body. To address this problem, the paper introduces a novel dynamic model in which the shell elements are employed to construct the thin-walled herringbone gears. The dynamic responses including gear flexibility are studied. Numerical results indicate that the proposed model shows good agreement with the finite element results in terms of natural frequencies and mode shapes. The noteworthy phenomenon observed is that the asymmetric error excitation and stagger angle will excite the transverse vibration of the thin-walled herringbone gear, which has never been obtained in previous research models. These results manifest the significance of the gear body flexibility modeling.