The rigid flexible coupling physical model of flexible aerocraft investigated in this paper. By introducing the theory of mechanics problems in a non-inertial coordinate system, the model with dynamic stiffening established, and it is clearly elucidate that, dynamic stiffening is a typical mechanics phenomenon in a non-inertial coordinate system. First, material mechanics and angular momentum principle are employed to establish continuous dynamic models of the subsystems. Then, based on the conclusions of orthogonalization of the normal constrained modes, the finite dimensional dynamic models are obtained. The numerical simulations show that, the first-order dynamic model established in this paper has considered dynamic stiffening. Thus, it could predict the dynamic responses of the flexible aerocraft with large accurately, and can be directly used in controller design.