Abstract: Microwave-induced borehole fracturing is regarded as one of the most effective approaches for enhancing permeability and relieving gas pressure in low-permeability coal seams. Owing to its high thermal efficiency, environmental friendliness, and non-contact characteristics, microwave fracturing technology demonstrates considerable potential for borehole-based coal fracturing and permeability enhancement. However, the fracturing characteristics and underlying mechanisms remain insufficiently understood. To address this issue, an open-ended microwave-induced borehole fracturing experimental system is developed, and a series of open-ended borehole microwave fracturing experiments are conducted. The fracturing process of coal subjected to open-ended microwave irradiation is clarified, and the relationships among microwave parameters, coal temperature evolution, acoustic emission characteristics, and crack propagation are established. The temperature rise behavior, crack initiation, and fracture propagation patterns of coal during microwave-induced fracturing are thereby revealed. Based on a thermo-mechanical coupling model for open-ended borehole microwave fracturing, the spatiotemporal evolution of temperature and stress fields in the coal surrounding the borehole is analyzed. The effective influence range of borehole microwave fracturing is determined, and the thermo-mechanical coupling mechanism governing microwave-induced coal fracturing under borehole conditions is elucidated. The results indicate that the thermal effect of open-ended microwave irradiation causes rapid heating of coal around the borehole, forming distinct temperature zones, namely the heating zone, heat-transfer zone, and unheated zone. This thermal heterogeneity induces intense tangential tensile stresses, leading to crack initiation at the outer boundary of the heat-transfer zone, pre-existing fissures, or free surfaces. Subsequently, cracks propagate continuously and coalesce toward the borehole, resulting in large-scale fracture development. High-power microwave irradiation accelerates temperature rise and thermal stress accumulation, significantly shortening the crack initiation period of the coal mass and slightly reducing the threshold temperature required for crack initiation. Consequently, rapid crack propagation is promoted, and the fractured zone around the borehole is markedly enlarged. With increasing irradiation duration, both the spatial extent of temperature zones and the magnitude of tangential tensile stress continue to increase, leading to a significant rise in the number, length, and aperture of newly formed cracks. Microwave-induced cracking enlarges the crushing zone of the coal mass surrounding the borehole and reduces its effective stress, thereby producing a pronounced pressure-relief effect. For example, under a microwave power of 14 kW and an irradiation duration of 400 min, the crack propagation radius reaches 1.57 m, while the pressure-relief radius reaches 2.72 m. These findings provide essential theoretical and technical support for the development of microwave-induced coal fracturing and permeability enhancement technologies and related equipment.