<p>Hot-stage polarizing microscopy technique was employed to investigate the mesoscopic fracture evolution characteristics of granite throughout the entire process from room temperature to real-time high temperature and then to cooling. The study analyzed the influence of mineral types, temperature, cooling medium, and the heating and cooling progress on the microcrack development in granite. Additionally, the contributions of heating and cooling to the damage of granite were discussed. The research indicates that crack evolution follows a characteristic trend: the number of small cracks increases, and larger cracks form through the coalescence and propagation of smaller ones during heating. The thermal fracture threshold for granite was identified at 300 °C. The three main minerals in granite exhibit distinct area change behaviors with temperature. After natural cooling, mineral areas show a slight increase compared to the pre-treatment state. Following thermal shock in water, these areas decrease marginally relative to their extent at 600 °C yet remain significantly larger values than initial ones. Thermal shock cooling induces more extensive fracturing in granite compared to natural air cooling. Furthermore, the heating process contributes more significantly to the overall damage than the subsequent cooling stage. This study enhances the understanding of mesoscopic evolution in thermal disturbances treated rocks and provides a theoretical basis for assessing rock stability in high-temperature engineering environments.</p>