Extensive use of lifting body, wave-rider aerodynamic layout and other composite materials, thin-walled structures, lead the frequency of structural vibration and rigid body motion very close. This yields a great challenge to the vehicle control system design. Taking into account the transverse displacement, a specific simplification which treats the vehicle body as two mass center fixed cantilever beams was adopted. And the hypersonic aircraft-s rigid body/elastic coupling model was derived based on the principle of virtual work and Lagrange equations. After comparing the open-looped poles of new coupling model and traditional rigid body model, a conclusion that the short-period vibration mode and the structures vibration mode tightly coupled with each other was made. The centrifugal force affected the height and long-period mode, and the effect on the flight path can not be ignored. Finally, changes in flight speed and structural damping on the dynamic performance of coupled model were analyzed. Results show that flight speeds significantly affect the rigid body motion modes, while the structural damping mainly changes in elastic mode.