An analysis on the principle of bracket used on small caliber automatlc gun is presented in this paper. A FEM dynamical model is established to slmulate the coupled movment of gun barrel and bracket. In the model , gun barrel and bracket are described as some elastic beam elements , shape function is used to describe the disturbing of these elements , and lagranglan equat10n IS used to educe the dynamical equations.A numerical simulation of the dynamical model is presented , and the analysis and discussmg based on the numerical results indicate that a properly designed bracket will be helpful to firing precision of small caliber automatic gun.