Abstract: Based on the engineering reality,a calculation model of the rotor blades hinge moment about coaxial helicopter was set up.An airfoil unsteady aerodynamic model was established by introducing a set of Leishman-Beddoes semi-empirical indicial response formula.The induced velocity model of the aerodynamic interaction between upper and lower rotors of a coaxial helicopter was created by introducing an interferential factor into the Pitt-Peters dynamic inflow model;the Runge-Kutta method was used to obtain the numerical solution of the rigid blade flapping angle,and a modal superposition method used to calculate the distortion of the flapping direction.According to analysis of the coaxial helicopter,the total hinge moment is basically the same,although the partial hinge moments of upper and lower rotors are different.In medium and high speed,the hinge moments of upper and lower rotors are accumulated at the lower swashplate to form a moment making the lower swashplate lean forward.