Abstract：In order to study the characteristics of rock crack,carrying on a scanning electron microscope( SEM) test on granite,marble and sandstone in the same microwave power 10 k W after irradiation and dropweigh test,the rock cracks fracture shape and morphology,the types of micro-cracks and micro-fracture model were studied,and the rock failure mechanism was analyzed at the same power and after drop-weigh test. The results showed that: from a macro sectional view it can be seen the development of cracks and color variation;through SEM microscopic observation of the fracture morphology,granite was flat and striped,marble was stepped,and sandstone was crushed shape and honeycomb; granite and sandstone microscopic cracks generated by tensile stress and compressive stress,while marble was condensation crack; granite fracture type was intergranular fracture,trans-granular fracture and the superimposed of the two,and marble was mainly along the grain fracture,and sandstone was mainly trans-granular fracture.

Keyword：scanning electron microscope(SEM);fracture morphology;microscopic cracks type;microscopic fracture model;