Aiming at the issue of large vibration loads during high-speed forward flight of coaxial helicopters， the implementation of high-order harmonic control（HHC） on the coaxial rotors system is considered for active vibration suppression control. In this paper， the classical moderate deflection beam structural dynamics model of rotor blades， the unsteady aerodynamic model of rotor with free wake， and the HHC active control model are innovatively and deeply coupled. A comprehensive aeroelastic analysis model for high-harmonic active control suitable for coaxial dual rotors is established. Based on the validated model， the XH-59A coaxial dual-rotor system is selected as the research object， and a systematic parametric analysis of the effects of HHC parameters， such as amplitude and phase， of collective pitch on the vertical hub vibration loads of the upper and lower rotors is conducted. The study shows that the hub vibration reduction effect of coaxial twin rotors first increases and then decreases with the increase of HHC amplitude. That is， HHC can effectively suppress the vertical vibration load of the hub under appropriate amplitude or phase conditions. Both 3/rev and 6/rev harmonics can significantly reduce the corresponding-order vertical hub vibrations， achieving a maximum reduction of up to 90%， although their influence on vibrations of different orders is limited.