Abstract: According to Navier-Stokes equation and Spalart-Allmaras turbulence model，the motion law of projectile under the action of high- pressure gas and its flow characteristics are simulated by using the dynamic mesh method based on CFD software. The change rules of in-bore average pressure， projectile base pressure， chamber base pressure and projectile motion parameters at the four kinds of initial pressure in the chamber are mainly studied. The changes of Mach number contours at different time at initial pressure up to 2.5 MPa are analyzed. Research results show that a flow oscillation phenomenon occurs in the bore，and the changes of chamber base pressure and projectile base pressure are fluctuating. Initial gas chamber has the effect on the pressure oscillation amplitudes of chamber base and projectile base and the projectile in the muzzle velocity. The relationship between projectile motion velocity or motion time and motion distance in the barrel is approximately parabolic.

Key words: ordnance science and technology, high-pressure gas, dynamic mesh, interior ballistic, muzzle flow field, computational fluid dynamics