Base on the half-open muzzle brake, a nozzle high-efficiency muzzle brake is designed. Draw out the level backwards Laval nozzle on two sides of the half-open muzzle brake, and use the high-pressure gas in chamber to achieve low recoil force, and compute interior ballistic trajectory. Base on the rigid-flexible coupling dynamic theory, the dynamic model of vehicle Gatling gun with nozzle high efficiency muzzle brake are made, and the numerical simulation is computed. The results show that the firing performance of gun system is improved when the recoil force, recoil displacement, muzzle angular displacement and projectile displacement decrease.