<p>Tensile failure in jointed rock masses governs the safety of underground excavations and hydraulic structures, yet the combined roles of joint inclination, joint roughness coefficient (<i>JRC</i>) and matrix strength under splitting conditions remain insufficiently quantified. Here we fabricate disc specimens with 3D-printed rough joint molds and cement-mortar matrices calibrated against field sandstone properties, and conduct Brazilian tests across seven inclinations (0°–90°), four <i>JRC</i> levels (4–16), and three matrix strengths. We further perform PFC2D simulations with geometrically prescribed roughness and a contact-weakening scheme on the joint plane to reveal microcrack evolution. Results show a hierarchy of sensitivity inclination &gt; matrix strength &gt; <i>JRC</i>; two critical inclinations (<i>α</i>_J, <i>α</i>_L) control transitions among Type I: matrix, Type II: combined, and Type III: joint plane damage. The observed intensity dips in normalized strength coincide with <i>α</i>_J and <i>α</i>_L, reflecting shifts in the tensile–shear microcrack ratio localized on the joint plane. Theory rationalizes how decreasing matrix strength lowers <i>α</i>_L, promoting earlier joint-plane dominance, whereas <i>JRC</i> mainly modulates crack kinematics at small–moderate inclinations and becomes marginal at 90°. The study provides a micro-to-macro framework for interpreting tensile behavior of jointed rocks under splitting.</p>