Abstract: The high geothermal gradient and elevated in-situ stress encountered in deep resource extraction significantly influence the mechanical behavior of reservoir rocks, posing considerable challenges for deep rock breakage. To elucidate the rock breaking mechanisms of abrasive water jet (AWJ) impact under the coupled effects of high temperature and confining pressure in deep formations, a series of jet impact experiments were conducted on granite samples subjected to temperature levels ranging from 25°C to 400 ℃ and confining pressures from 0 to 40 MPa. Five temperature gradients (25, 100, 200, 300 ℃, and 400 ℃) and five confining stress levels (0, 10, 20, 30 MPa, and 40 MPa) were considered. A laboratory-scale water jet platform was used to conduct the impact tests, combined with computed tomography technology (CT), 3 dimensional reconstruction, and scanning electron microscopy (SEM) to comprehensively investigate the macro-breaking characteristics, crack evolution, and microscopic failure morphology of granite under varying loading conditions. Results demonstrate that increasing temperature deteriorates granite integrity and enhances its breakability. Complex crack networks appeared above 200 ℃, and structural integrity was severely compromised at 400 ℃. At zero confining pressure, the erosion depth at 400 ℃ increased by 82.1% compared with room temperature, while crack volume and area rose by factors of 88.2 and 114.6, respectively. Conversely, confining pressure strongly inhibited fragmentation: at room temperature, raising confining pressure from 0 to 40 MPa reduced penetration depth by 60.7%, with crack volume and area decreasing by 49.9% and 49.1%, respectively. The coupled effects of temperature and confining pressure exhibited a nonlinear response. While confining pressures below 30 MPa suppressed jet-induced damage, the combination of high temperature (400 ℃) and high confining pressure (40 MPa) unexpectedly promoted crack growth. The three-dimensional reconstruction results based on CT scanning indicated that the critical temperature range for changes in crack spatial distribution is between 200 ℃ and 300 ℃ under no confining pressure, and the crack volume and area grow rapidly once the range is exceeded, whereas this critical temperature range is delayed to 300～400°C under 40 MPa confining pressure. SEM observations further revealed typical fracture features such as abrasive indentations, intersecting thermal cracks and shear erosion, ploughing grooves, and fragment spalling, reflecting the combined action mechanisms of abrasive erosion, thermal stress, and fluid scouring. This study revealed a mechanism transition of abrasive water jet rock breaking under thermo-mechanical coupling, evolving from abrasive-dominated erosion to thermo-mechanical synergistic fragmentation, and suggested that thermal degradation of rock and thermo-mechanical stresses induced by fluid–solid temperature differences can be exploited to reduce the energy consumption of AWJ rock breaking in deep formations, while the jet parameters should be optimized in accordance with confining pressure to avoid inhibition of crack propagation and improve the rock breaking performance.