Abstract: Testing the mechanical response of ultra high-performance concrete (UHPC) at high pressure is essential for predicting its penetration depth and residual velocity of the projectile. This study designed and fabricated a uniaxial strain testing device capable of applying passive confining stress of 800 MPa using high strength steel. The uniaxial strain test of UHPC was performed, obtaining the hydrostatic pressure-volumetric strain and the hydrostatic pressure-equivalent stress relations within a high hydrostatic pressure range of 1 GPa. The strength surface and equation of state parameters of the Holmquist-Johnson-Cook (HJC) model were calibrated for UHPC based on test results, which were validated as accurate through simulation of the uniaxial strain test using LS-DYNA. The numerical model of a previous penetration test of UHPC was established using the calibrated HJC model. The parametric analysis of mesh size and erosion criterion reveals that it has a converged penetration depth independent of the erosion criterion or mesh size. The penetration test of UHPC, including 28 scenarios at impact velocities ranging from 428 m/s to 1115 m/s, was simulated using the converged finite element model. It shows that the calibrated HJC model accurately reproduces the penetration depth and residual velocity of the projectile in contrast to experimental observations. The established prediction method based on uniaxial strain response is crucial for assessing the penetration resistance of UHPC protective structures.