Abstract: Ultra-high performance concrete (UHPC) is a new construction material with a super high level of strength, toughness and resistance. Hence, a systematic study on the mechanisms of UHPC against a scaled earth penetrator is of great significance to enhance the anti-penetration ability of military protection engineering and ensure the safety of lives. In this paper, the ballistic smoothbore gun was used to carry out a series of penetration tests on the C40 ordinary concrete and C180 UHPC with speeds of 500m/s and 850m/s, respectively. In addition, a penetration process was simulated by the LS-DYNA software with the test data. Results show that the UHPC notably decreased the damage to targets caused by the projectile, efficiently reduced the penetration depth and restricted the depth and diameter of craters, which was superior to ordinary concrete in the performance against penetration. In the process of numerical simulation, the key parameters of the HJC model under the dynamic impact effect was determined. The simulation results agreed well with the test data, suggesting the selection of the parameter was reasonable, which provided detailed data for the analysis of the anti-penetration mechanisms of UHPC.