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Microwave-assisted mechanical rock-breaking can effectively solve the problems of low efficiency of hard rock-breaking and severe wear and tear of equipment. This study used granite as the research object and analysed electromagnetic–thermal characteristics and dynamic tensile characteristics of microwave-irradiated granite. The microwave irradiation problem was decomposed into the electromagnetic–thermal unidirectional coupling and thermal–mechanical unidirectional coupling problems for numerical solutions, and the weakening mechanism of microwave irradiation was discussed at the microscopic level. The results showed that the thermal stress generated by the rapid heating and selective heating characteristics of microwave irradiation is the dominant factor in microwave fracturing. The presence of thermal cracks affects the crack extension path, making the failure more complicated. Tensile failure is the primary mechanical mechanism that causes the macroscopic fracture of the specimen, and intergranular failure dominates the overall failure of the specimen. Microwave irradiation reduces the shear resistance of the specimen. Microscopically, the proportion of shear cracks gradually increases with the increasing of irradiation duration (TM). Macroscopically, the area of the wedge-shaped failure zone gradually increases. [ABSTRACT FROM AUTHOR]