Abstract: The impact of bolt during locking time is the fatigue source of fatigue rupture of breech mechanism components. In this paper, the bolt of a gatling gun was used as the research object, a finite element model of components such as bolt head, bolt body and receiver rails during locking time was established. The transient dynamics analysis of the bolt under high bore pressure dynamic load was carried out. The equivalent stress analysis of the weak spots of bolt was carried out. And utilizing the nCode DesignLife, fatigue life analysis of bolt based on fatigue design method of nominal stress method and time step load mapping was conducted. In addition, fatigue result nephogram of bolt and fatigue life of every node were obtained. The simulation results show that the bolt does not produce plastic deformation during the locking process and the fatigue life is greater than the actual services life. The simulation results conform to the life design requirements of the gun and provide reference for the improvement of bolt of similar gatling gun.