Abstract: To investigate the efficiency and mechanism of breaking heterogeneous rocks using a combined water jet and cutter tooth under high-stress conditions in deep complex formations, a numerical model was established based on the smoothed particle hydrodynamics-finite element method, taking sandstone composed of quartz, feldspar, and calcite as the research object. Four rock-breaking modes were studied: single-tooth breaking of homogeneous rock, single-tooth breaking of heterogeneous rock, water jet combined with single-tooth breaking of heterogeneous rock along different trajectories, and along identical trajectories. The damage and time-dependent characteristics of heterogeneous rocks were analyzed, and the evolution pattern of damage energy in loaded rock was examined to reveal the damage mechanism of heterogeneous rocks under the combined impact of water jet and cutter tooth. The results showed that when heterogeneous rocks were broken by the combined action of water jet and single cutter, damage-prone zones formed in low-strength components and at component interfaces, which tended to induce the initiation and propagation of main cracks under stress concentration, resulting in large-scale severe damage zones. The rock-breaking modes along different and identical trajectories showed respective advantages in rock-breaking width and depth. From the perspective of overall rock-breaking area, the different trajectory mode was superior. Under the combined action of water jet and cutter tooth, the damage energy variation of the heterogeneous loaded rock was mainly in the form of internal energy, whose peak occurred earlier than that of kinetic energy. High-strength components facilitated internal energy accumulation. The initial damage of heterogeneous loaded rock was mainly caused by compressive-shear stress, followed by instantaneous damage under the combined effects of dominant compressive-shear stress, auxiliary tensile stress, and stress concentration.