Abstract: To improve the rock-breaking efficiency of deep dry hot rock, taking granite, a common lithology of dry hot rock formation, as the research object, the changes in the mechanical properties of granite under ultra-high temperature was proposed. In view of the limitations of laboratory experimental methods, the Brazilian disc splitting numerical model of high-temperature granite was established by using numerical simulation and theoretical calculation methods, and the distribution characteristics and disturbance mechanism of stress field of hard granite under temperature-pressure conditions were investigated. It is found that under uniaxial and radial compression load, the stress distributions of high-temperature granite get significantly disturbed, leading to lower tensile stress along the horizontal direction, smaller compression and shear effect near the loading points, and easier fracture conduction. The higher the temperature, the more obvious the rock damage and the lower the tensile strength of the rock. The results reveal the evolution law of mechanical properties of granite under the effect of temperature, which can provide theoretical basis for efficient development of deep dry hot rock resources.