The real development of hot dry rock(HDR) geothermal is deep HDR geothermal. Because of different diagenesis environments, the mineral composition and micro-structure of deep granite are quite different from those of shallow granite. To reveal the real characteristics of deep granite and guide HDR geothermal development, the difference of thermal and mechanical properties between the granite in Luya Mountain, Shanxi Province, China(coarse-grained granite) and the granite in Shandong Province, China(fine-grained granite) under triaxial stress at high temperature(100-400 ℃) was studied. The results show that the thermal expansion coefficient of coarse-grained granite increases linearly with the increase of temperature, and the thermal expansion coefficient of coarse-grained granite is 1.52 times that of fine-grained granite on average, and the difference between them reaches the maximum at 400 ℃. The elastic modulus of coarse-grained granite increases first and then decreases with the increase of temperature, and its threshold temperature varying with temperature is 300 ℃. The elastic modulus of fine-grained granite is 1.4～2.6 times that of coarse-grained granite, and the difference increases with the increase of temperature and confining pressure. Micro-observation shows that the large number of preexisting fractures and extreme heterogeneity in coarse-grained granite lead to larger thermal deformation and more deteriorated mechanical properties of coarse-grained granite, and further make coarse-grained granite has higher permeability under high temperature and high pressure. This provides a good geological foundation for high efficiency, low cost and large-scale construction of artificial reservoirs in the process of HDR geothermal development.