Natural rocks are composed of many rock-forming minerals of uneven size, which have an important impact on the effect of microwave rock-breaking. In order to explore the influence of mineral particle size distribution characteristics on rock irradiability, this paper extracts the particle size distribution characteristics of typical granite minerals to determine the particle size unevenness coefficient of granite minerals. Through indoor tests, we carry out research on the influence of particle size distribution characteristics on rock temperature, cracks, strength and P-wave velocity. To further analyze the influence mechanism of particle size distribution characteristics, a numerical analysis model was established using the multi-physical field COMSOL analysis platform to analyze the distribution and evolution of the stress field, temperature field and plastic zone of the specimen after microwave irradiation. The research shows that the inhomogeneity of mineral particles in the rock significantly affect the temperature and distribution of rock samples. The greater the mineral inhomogeneity, the higher the rock surface temperature, however, the rate of temperature increase gradually diminishes as the irradiation time extends.The greater the non-uniformity coefficient of mineral particle size distribution, the more new cracks and potential cracks will be generated after microwave irradiation, the greater the decrease in P-wave wave velocity, the higher the strength loss rate of the sample, and the more obvious the weakening effect of microwave rock; The larger the non-uniformity coefficient, the greater the critical stress zone and the plastic zone area; the plastic zone first appears at the junction of potassium feldspar and quartz.