In order to study the effect of multi-chamber on the recoil efficiency of the device, a closed reflective expansion device with three chambers and multiple reflectors was designed, and numerical simulation was carried out based on three-dimensional unsteady N-S equations and dynamic mesh technology. The force of the device is determined by simulation, and the change law of the self-braking efficiency and the muzzle overpressure is explored after the device is matched with the muzzle brake. The calculation results show that the force of multi-chamber is significantly higher than that of single-chamber, which is more conducive to improving the efficiency of the device, and the muzzle overpressure can be effectively reduced by adjusting the parameters of the inlet hole. It has a certain reference value for the further design of the device.