Significant potential exists for mining hot dry rock in coastal areas, oceans, islands, and reefs by utilizing abundant seawater as a heat-exchanging medium. It is crucial for optimizing reservoir stimulation technology to explore mechanical characteristics and mechanisms for damage of reservoir rocks during seawater mining of hot dry rock. In this research,granite was subjected to several heat treatment temperatures (100 to 500 ℃) and various numbers of fatigue thermal shocks (0-20) using seawater before Brazilian splitting tests and acoustic emission testing. The findings show that temperature, the thermal shocks, and seawater dissolution are the main factors influencing granite’s tensile strength.The temperature threshold for significant degradation of tensile strength, resulting from thermal shock from seawater and heat treatment, ranges from 200 to 300 ℃. At high temperatures (300 to 500 ℃), seawater decreases the tensile strength of granite by approximately 1.67 times compared to freshwater in cycles 0-10, and by about 3.20 times in cycles 10-20. In general, the higher the temperature and frequency of seawater impact, the greater the plasticity of the rock, the lower the tensile strength, and the higher the cumulative count and energy of acoustic emission. The number of seawater thermal shocks and granite’s tensile strength have a negative link that is substantially amplified by the temperature. The double effects of seawater cold cycle and heat treatment temperature cause granite to become more porous and progressively shift from tensile to shear damage. These results provide a benchmark for utilizing seawater as a thermogenic medium in enhanced geothermal systems for mineral extraction procedures.