Abstract: The high geothermal environments encountered in deep mineral mining induce thermal damage to rocks, which can trigger geotechnical disasters in deep engineering projects. Therefore, exploring the degradation characteristics of rock mechanical properties and the damage evolution laws after high-temperature exposure is of significant importance for rock engineering in deep high-geothermal environments. By subjecting granite to the temperature range from ambient to 1200 ℃ and conducting macro-microscopic studies using optical microscopy, the degradation characteristics of Young's modulus and compressive strength in granite samples post various high-temperature treatments were investigated. Additionally, an analysis was performed on the internal cracks and damage evolution in thermally damaged granite from a microscopic perspective. The experimental results demonstrate that high-temperature treatments significantly reduce the mechanical properties of granite. The granite's compressive strength and Young's modulus decrease with increasing treatment temperatures, and the extent of crack development increases with temperature. The mechanic cal properties of granite are highly correlated with the development of internal crack structures. There is a power function relationship between the crack density and compressive strength in granite after different temperature treatments, indicating that crack density can effectively reflect the extent of thermal damage in granite.