Abstract: Pre-treatment of rock by microwave technology can weaken the mechanical properties of rock. To investigate the damage law of granite under different microwave heating methods, two kinds of electromagnetic-thermal-mechanical coupling numerical model, incorporating damage variables of rectangular waveguide and coaxial microwave heating, are established in this paper. The distribution law of electric field, granite temperature distribution law, stress distribution law and damage area change law under different microwave actions are analyzed. The results show that the coaxial microwave heating method can effectively feed the microwave into the interior of granite and irradiate more precisely than the rectangular waveguide; Both microwave heating methods induce tensile stresses within the height range of the borehole, creating a stress state characterized by "internal compression and external tension" beneath the borehole; The damage area morphology of coaxial microwave heating can connect the damage zone inside and outside the borehole, but the scope of the damage area is small. Conversely, the rectangular waveguide heating method can produce a wider damaged area in a shorter duration, but the damage area is not focused, and the damage areas inside and outside the hole are not connected. These findings show that the coaxial microwave heating method is recommended for accurate microwave radiation in a specific area of the borehole, and the rectangular waveguide microwave heating method is recommended for rapid acquisition of large damage areas and weak rocks.