<p>During the excavation of deep hard rock tunnels, the presence of crustal stress affects the load-bearing capacity and deformation failure mechanism of the rock mass, thereby influencing the rock-breaking efficiency. However, the rock-breaking mechanism and laws of the double cutters under confining stress are currently unclear. Therefore, by utilizing the hybrid finite–discrete element method to compare and analyze the numerical simulation results of breaking hard rocks with double cutters under different confining stresses, the breaking mechanism and laws of the double cutters for hard rocks under different confining stresses are analyzed. The results show that the normal force, crushing zone, large rock debris, radial cracks, lateral cracks, and symmetrical cracks are closely related to the changes in confining stress. The changes in the radial crack crushing characteristics under confining stress are related to the rock failure under shear action. The generation of large rock debris shifts from tensile failure to being dominated by shear failure, leading to the accumulation of energy inside the rock and causing rock bursts. The accelerated and continuous expansion of symmetrical cracks is caused by the redistribution of internal shear stress in the rock, while the initiation and expansion of cracks occur due to compressive stress.</p>