Aiming at the problem that a new generation of sub-caliber ammunition with sabot, which will be used in a 100mm naval gun, and which requires the retractor expansion chamber to have enough expansion volume, and also ensures that the sabot of the sub-caliber projectile can"t collide with the muzzle device, the main dimensional parameters of the muzzle retractor and the corresponding parameter variation ranges have been determined with the reference to the standards of the weapon industry and the actual working conditions. Meanwhile, two methods of theoretical calculation analysis and fluid simulation analysis are used to analyze the retracting efficiency of the muzzle retractor with different lengths of impact baffles in different numbers of chambers, and a muzzle retractor suitable for this 100mm gun is designed. It provides a reference for the design of other naval gun muzzle retractors.