T he f inite segment method is used for computing the elastic deformation of an ant iaircraf t gun barrel. The dynamic model of the gun with 7-rigid-body and 18 degrees of f reedom is established by means of Huston’ s method based on Kane. s equations. The numerical result s show that the angle displacement of the muzzle is larger than that of the dynamic model w ith 5-rigid-body and 10 deg rees of freedom. The gun-chest back-lash curves figured out by the tw o models are ex act ly consistent, and they are in agreement w ith the measured curves, w hich proves that the abovement ioned analysis is right, thus prov iding a more strict theoret ical inference for the precision analysis of the ant iaircraf t.