Aiming at the problems that the barrel length and recoil force of small bore gun do not match the unmanned combat platform, and the traditional muzzle device has a single function, a multi-functional muzzle device integrating recoil control, noise reduction and flame reduction was designed, and an overpressure distribution model suitable for the muzzle device was proposed. The muzzle flow field of a truncated gun barrel is calculated by using Fluent software to establish a two-dimensional axisymmetric gas dynamics model; The results show that the recoil efficiency of the muzzle device is 70%, the noise reduction rate is 17. 8%, and the error of the recoil efficiency and the noise reduction rate is 14% and 11% respectively. The results of numerical simulation show that the muzzle device can effectively reduce the recoil force of the gun, and has good concealment when firing, which meets the needs of modern warfare.