Abstract: During the production qualification test, the primer body of an armor-piercing shell fractured. In order to find out the failure cause, the design of primer body was recalculated, the production process was checked, and macro and micro observation, microstructure examination and hardness testing were carried out. In addition, damage simulation testing was performed by reducing the size of the tool withdrawal groove area. The results show that because of the effect of excessive torsion and axial tension during the process of assembly, micro cracks initiated at the thread root, resulting in fracturing of the primer body during the process of shooting. Based on the analysis result, some measures were put forward to improve the strength design and ensure proper assembly. As a result, similar primer failures have been prevented.