For the rocket pressurization system,safety pneumatic valve is a security device which protects the propellant tank from overpressure. On a ground test,the main valve revealed a phenomenon of flutter as the valve opening or closing,which may induces damage to some parts,what′s worse,threatens the product performance. To find out the cause of valve flutter, based on fluidstructure interaction of N-S dynamic grid flow equation of and nonlinear contact rigid body motion control equation,aerodynamic load is computed by Realizable k-ε turbulence model and explicit dynamic algorithm. The mechanism of valve flutter phenomenon is pressure fluctuation coupling with structural frequency and piston rod produces plastic deformation under impact response with position bolt. An improvement measure to improve structural frequency is increasing the size of moving parts. Following with ground test verification,the result shows that the measure being taken can suppress the safety pneumatic valve flutter effectively,which has practical engineering value.