Abstract: Geothermal energy has long-term strategic significance to relieve energy pressure in China,and accurately understanding the damage and fracture behavior of granite after thermal treatment plays a key role in the development of geothermal energy.Therefore,the grain-based model (GBM) in particle flow code (PFC^2D)was used to simulate the uniaxial mechanical behavior of granite after thermal treatment,and then the distribution characteristic of thermal crack,the variation of strength and deformation with temperature,and crack propagation process were analyzed.The result shows that GBM can reflect the variation of strength and fracture characteristic with confining pressure and temperature,the distribution of inter-granular crack transformed from dispersion to coalescence and then formed the macro-crack with increasing temperature.More inter-granular cracks can be observed when T=600℃.Under room temperature,the inter-granular cracks dispersedly distributed in the specimen under initial uniaxial loading.However,sliding between grains occurred during the loading process due to more thermal cracks existing in the specimen when T=600℃.After the peak strength,the macro failure occurred due to the propagation of intra-granular cracks.The damage and degradation mechanics in micro scale was investigated in this work,which of significant to ensure geothermal exploitation.