A wind tunnel fluctuating pressure test method using the aeroelastic scaled model of a launch vehicle is established. The aeroelastic scaled model is similar to the launch vehicle in geometry and reduced frequency. A wind tunnel test using both the rigid scaled model and aeroelastic scaled model of a hammerhead launch vehicle is conducted to measure fluctuating pressure on the model surface and to evaluate the influence of vibration on unsteady pressure. The Mach number of the test is 2.5. Test results suggest that the flow field of the rigid model has no characteristic frequency while that of the elastic model at a small angle of attack encounters dominant frequencies which are exactly the first order model structural frequency and its multiplication. Moreover， the root-mean-squares of fluctuating pressure increase tremendously when fluid structure interaction occurs. At a high angle of attack， the root-mean-squares of fluctuating pressure on the elastic model decrease to the level near the rigid model results as the fluid structure interaction weakens. The strain at the base of the elastic beam is measured and the result shows a half cycle phase difference between the vibration and the pressure signal of the 1st order characteristic frequency at the divergent stage. Finally the interaction between the pressure and structure reaches a limit cycle oscillation stage and the phase difference decreases to nearly zero. These phase differences have an impact on the capacity of doing work on structure by flow.