<p>During helicopter operations, continuous pilot control adjustments induce variations in aerodynamic parameters, which are subsequently transmitted to the transmission system through changes in engine output and main/tail rotor loads, thereby influencing the dynamic behavior of transmission system. To elucidate the influence patterns of pilot control parameters on helicopter transmission system dynamics, this study establishes a comprehensive rotor–engine–transmission coupled dynamic model. The helicopter flight dynamic model is developed based on a linear quasi-steady blade element aerodynamic model and uniform induced velocity theory. The engine thermodynamic model is formulated using the component-based method, while the transmission system is modeled via the lumped-parameter approach, incorporating internal and external excitation sources. A fully coupled dynamic framework is established and solved numerically using the Newton–Raphson algorithm, the finite difference method, and the Runge–Kutta integration scheme. Furthermore, parametric studies are conducted to systematically evaluate the effects of key control inputs—including main rotor and tail rotor collective pitches, as well as lateral and longitudinal cyclic pitches—on the dynamic characteristics of the transmission system. The results reveal that these control parameters significantly modulate the vibration amplitudes and dynamic load distribution, although they do not alter the quasi-periodic nature of the torsional meshing vibration. This work provides a robust theoretical foundation for the design and performance optimization of helicopter transmission systems under complex flight conditions.</p>