3D printed concrete is a promising new construction technology with potential applications in military field. As a prerequisite for its application in the military field, 3D printed concrete should possess strong impact resistance, providing reliable protection for military equipment and personnel. Currently, experimental research on the impact resistance of 3D printed concrete is limited by cost issues. Therefore, the use of numerical simulation technology can improve research efficiency, reduce costs, and better reflect the failure processes and damage conditions of 3D printed concrete. However, current numerical simulation technologies for 3D printed concrete do not take into account its unique interface structure, and thus fail to fully reflect the mechanical properties of 3D printed concrete. Based on the results of chloride ion penetration experiments, this study quantitatively characterizes the proportion of the interface region in 3D printed concrete. Using this as a basis, and in conjunction with previous mechanical performance studies, a numerical simulation model for the penetration resistance of 3D printed concrete was established, and its failure behavior was further investigated. By comparing the numerical simulation results with penetration experiment data, it was found that the penetration depth error of the 3D printed concrete model is within 4%, demonstrating its high simulation accuracy. During the penetration process, the 3D printed concrete target exhibits a characteristic of damage concentration at the interface, with the energy absorption at the interface being greater than that in the non-interface regions. As the projectile velocity and target strength increase, the projectile may disintegrate during penetration, leading to a sudden reduction in penetration depth, which further affects the variation of projectile velocity during the penetration process. Measures such as interface reinforcement, improvement of the 3D printing process, and the addition of high-strength aggregates can effectively reduce the penetration damage depth of 3D printed concrete targets, thereby enhancing their penetration resistance.