Abstract: A model of three-barrel gun including high speed projectiles was presented, the dynamics process of muzzle flow with projectiles was simulated by using AUSM scheme with N-S equation, and large displacement boundary of dynamic mesh, method were employed to solve the Spalart-Allmaras. According to the predicted results, the blast wave patterns and development of the powder gas flow field in the vicinity of the muzzle were analyzed in detail to reveal the interrelationship between flow field and projectiles based on the numerical results. The results can be used for provide necessary basis of prediction in firing accuracy of multi-barrel gun weapon system.