The closed belt of the ammunition feeding system without a chain typically adopts a chain drive structure, which presents complex vibration characteristics during firing. This paper proposes a dynamic analysis of the closed belt. Based on the Dubowsky impact pair model to simulate the gap collision effect, measures are taken to simplify the connection between concentrated masses, concentrated masses, and sprockets into a spring and damping system. Using bond graph theory, a bond graph model of the linear closed belt is established, and the state equation of this model is solved to obtain the influence of gap size on the dynamics and vibration of the linear closed belt. The results show that this study can provide a reference for the dynamic modeling of closed belts with gaps and their lateral vibration analysis.