<p>The process of free-surface rock failure by a disc cutter and the influence of breaking parameters on rock fragmentation performance were numerically investigated. The propulsive force of the disc cutter and the resulting rock fragments in the numerical model showed good agreement with experimental results, indicating that the validated model successfully reproduced the free-surface rock failure process. Crushing pits were formed under the compressive stress induced by the disc cutter, while crack initiation and propagation toward the free surface were dominated by tensile stresses, forming fan-shaped fragments during the breakage process. The relationships between breaking parameters (wedging depth, inclination angle, and tip width of the disc cutter) and rock fracture characteristics (fragment size, peak penetration force, and specific energy) were obtained and analyzed. Research findings: The propulsive force of the disc cutter and the rock fragment size increase monotonically with wedging depth, while specific energy decreases, with 20 mm identified as the optimal wedging depth. The critical penetration depth decreases linearly with increasing inclination angle, and both the propulsive force and specific energy reach their minimum at an inclination angle of 35°. Tip width has little effect on fragment size, but the propulsive force increases linearly with tip width. The lowest specific energy is achieved with a 1.5 mm tip width. The pre-slotting rock breakage method significantly reduces the peak propulsive force compared to the conventional method. The influence of pre-slotting depth on rock fracture characteristics was also investigated, and results show that pre-slotting can enhance the rock-breaking performance of disc cutters, suggesting it as a promising method for efficient hard rock excavation.</p>