Gun’s vibration is significant for the firing accuracy, which has been a classical problem concerned for long time due to particularity of the shock excitation and complexity of the mechanism system, it is the dominant research branch to establish a dynamic model approaching the true movement of gun and to obtain the vibration characteristic under the various excitations corresponding to such a problem. This paper develops the modeling methods for gun’s vibration based on the dynamics of the rigid bodies and multi flexible bodies systems respectively by Lagrange equation and Gaussian variational principle, and uses the rigid models and rigid flexible coupling models to analyze gun’s vibration. Besides, the vibration response of gun system to the shock is simulated and the natural vibration characteristic is treated for the gun’s mechanism. Finally, the amplitudes variety of the vibration with the structural parameters of gun are obtained. The research results indicate the mechanism for improving the vibration performance of gun to increasing the firing accuracy, and have value to engineering application.