The knowledge of Fluent and dynamic mesh was used to establish simulative model for a three-gun cluster weapon, based on the influence of delayed firing, and the N-S equation was calculated to simulate the process of muzzle flow field influenced by multiple coupling and delayed firing. Compared with the numerical simulation of correctly shooting, the influences of flow field and the projectile are mutual; The projectile posture is more deteriorated than the normal firing with consideration of the influence of delayed firing and the shooting precision has a large drop. The simulation results have important value for the command of the shooting of cluster weapon.