Abstract: To investigate the potential of supercritical carbon dioxide (ScCO₂) as a heat-carrying fluid in Enhanced Geothermal Systems (EGS) and its impact on the mechanical properties of hot dry rock (HDR) reservoirs, this study conducted interaction experiments between ScCO₂/distilled water and deep granite from the Matouying Uplift area in Tangshan. Experiments were performed under conditions of 30 MPa pressure and temperatures of 150 ℃, 180 ℃, and 210 ℃. Changes in mineral composition, porosity, elastic modulus, and hardness of the granite before and after ScCO₂-water-rock reactions were comparatively analyzed using X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), nanoindentation testing, and aqueous ion concentration analysis. The mechanisms by which ScCO₂-water-rock reactions influence the micro-mechanical properties of the granite were explored. The results indicate that: ScCO₂-water-rock reactions did not significantly alter the mineral composition of the granite. However, the dissolution rate increased with rising temperature (from 150 ℃ to 210 ℃), rising from 0.3% to 1.62%. Post-reaction, the total pore volume and the pore volumes within all pore size fractions except mesopores generally exhibited an increasing trend. The inflection point phenomenon in the mercury intrusion curves weakened, indicating enhanced pore connectivity. Furthermore, pore connectivity increased with temperature. Total pore volume and macropore volume increased, while changes in pore volumes within other size fractions showed no clear trend. With increasing reaction temperature, the elastic modulus and hardness of the granite decreased by approximately 33% and 39%, respectively. The ranking of mechanical stability among the different minerals was: Quartz > Feldspar > Biotite. The rock's elastic modulus and hardness correlated with the content of rigid matrix components (e.g., quartz, feldspar). This study demonstrates that the stable mechanical performance of quartz minerals is fundamental to maintaining the micro-mechanical stability of the granite. Conversely, the dissolution of feldspar minerals leads to microcrack propagation within the minerals and the destruction of cementing structures, or the formation of secondary clay minerals (e.g., kaolinite), representing the primary cause of granite strength degradation. Simultaneously, the formation of clay minerals from biotite dissolution further deteriorates the micro-mechanical properties of the granite.