<p>The heterogeneous layered metamorphic rock contains both foliation and defects. To investigate the influence of foliation and defect orientations on the mechanical behavior and tensile fracture anisotropy of rocks, Brazilian Splitting Tests and numerical simulations were conducted on intact gneiss with different foliation orientations (<i>θ</i> = 0–90°) and pre-cracked gneiss with different deflection orientations (<i>α</i> = 0–90°), combined with Digital Image Correlation analysis. An improved Grain-Based Model (GBM) was developed. By adjusting the spatial orientation of particle arrangements, the model simulates foliation directions and accurately identifies and classifies crack patterns and quantities, enabling a more realistic representation of the fracture behavior of heterogeneous rocks. The results of this model indicate that the orientations of foliation and defects have a significant influence on the tensile strength of the specimens. For the intact discs, as the foliation angle increases, the number of inter-grain cracks decreases, and the tensile cracks remain aligned with the foliation direction. The proportion of tensile cracks first decreases and then increases, reaching the minimum (62%) at <i>θ</i> = 45°. For the pre-cracked discs, as the pre-cracked deflection angle increases, the number of intra-grain cracks first increases and then decreases. The proportion of tensile cracks drops from 93% at <i>α</i> = 0° to 37% at <i>α</i> = 90°, while shear cracks gradually concentrate along the deflection direction and become dominant in the failure process. <i>E</i>_xx strain evolution cloud maps show that when the pre-cracked deflection angle approaches the foliation angle (<i>α</i> = 0°, 15°, and 30°), the crack coalescence point occurs near the middle of the prefabricated crack.</p>