3D Concrete Printing (3DPC) enables the fabrication of geometrically complex lattice structures, and Selective Paste Intrusion (SPI) technology further extends this capability to precisely control internal architectures. This study presents the first numerical validation of the mechanical performance of SPI 3DPC lattice structures at the specimen scale. A finite element framework based on the Concrete Damaged Plasticity (CDP) constitutive model was established to investigate compressive responses of gyroid geometries with varying volume fractions. The results demonstrate good agreement between the numerical model and experimental data in terms of elastic modulus and compressive strength. The simulations also reveal a transition in the localization pattern with increasing volume fraction, from nodal strain localization in the 40% specimen to a continuous diagonal shear band in the 60% specimen, consistent with experimental crack patterns. Parametric analyses further indicate that tensile and compressive strength govern peak capacity, while elastic modulus controls initial stiffness and fracture energy regulates post-peak softening behavior. The viscoplastic regularization parameter is also investigated for its effect on numerical convergence. The proposed framework provides a useful numerical tool for analyzing the mechanical response of SPI 3DPC structures and offers a basis for parameter calibration, structural response assessment, and future multiscale modeling.