Abstract: The formation and expansion of hard rock fissures is an important part of studying the mechanism of rock damage. In order to explore the expansion law of rock fissure which provided a theoretical basis for microwave-assisted rock breaking technology under microwave irradiation, scanning electron microscopy (SEM) equipment that can help to analysis the shape of the fracture, the type of fracture and the fracture model is a is used to scan the granite specimens after microwave irradiation and uniaxial compressive strength test. The results show that the color change of the surface of the test piece is accompanied by tensile cracking after high-power microwave irradiation. The upper part of the test piece is broken in powder form after the compression test. The morphology of the fracture surface of the granite is mainly flat under SEM equipment. Surface and stripe fractures; the crack types of granite are mainly tensile cracks and compression shear cracks; the fracture models of granite are mainly intergranular fractures, transgranular fractures and superposition of the two.