Because of the increasing trend of aspect ratio in missile design nowadays, the problem of pneumatic servo elasticity attracts the attention of designers. The pneumatic servo elasticity problem is caused by the unsteady aerodynamic force on the surface of missile with large aspect ratio, the coupling between missile structural elasticity and flight control system. Based on this, the pneumatic servo elasticity problem of missile is introduced in this paper. Considering the coupling effect between rigid body motion and elastic body motion, the additional aerodynamic force and moment caused by elastic vibration are derived, and the thrust eccentricity caused by elastic body deformation is considered. The eccentricity problem is simulated and analyzed by the elastic missile dynamic model, and the relevant conclusions are obtained.