Abstract: A grain-based model(GBM) of monomineral quartzite is constructed using the framework of particle discrete element calculation. The elastic modulus and boundary strength parameters of the mineral model are optimized using the development law of microcracks in quartzite as constraints. This model is used to study the meso-mechanism of high-temperature damage and strength deterioration of quartzite under thermal-solid coupling. The following conclusions are drawn: (1)The microcrack evolution law of quartzite under high temperature can be well reproduced by optimizing mineral elastic modulus and boundary strength parameters. Microcracks first germinate from the boundary of quartz grains and gradually extend to their interior, eventually forming a crack network. (2)In uniaxial compression simulations, the elastic modulus of quartzite initially increases and then decreases with rising temperature. Poisson's ratio follows an inverse pattern, decreasing at first and then increasing. Poisson's ratio is more sensitive to thermal damage than the elastic modulus. (3)As temperature increases, the discreteness of microcracks in quartzite increases. The failure mode gradually shifts from multi-slope shear failure to dispersed tensile(splitting) failure without obvious macroscopic cracks. (4)The mechanical strength deterioration of rock is closely related to its compactness, mineral composition, and content. The thermal damage temperature threshold of quartz rock is higher than that of granite, at approximately 200 ℃. (5)Thermal damage results from three types of rocks with different quartz content show that thermal fracture first occurs in minerals with low mechanical strength. The mosaic structure between minerals can inhibit the thermal damage of quartz minerals.