The mechanical properties of underground rock joints are significantly affected by high temperatures associated with geothermal fields. Consequently, investigating the mechanical properties of joints subjected to high-temperature cyclic heat treatment has become a crucial research focus. Granite joints with similar roughness were exposed to cyclic heating and air-cooling treatment at 400℃ for varying cycles. Direct shear tests were subsequently conducted under different normal stresses to explore the change of shear mechanical properties with increasing heat treatment cycles. Additionally, scanning electron microscopy (SEM) was utilized to elucidate the micro-mechanisms underlying the high-temperature effects. The experimental results indicate that as the heat treatment cycles increases, the peak shear strength and the variation in the joint roughness coefficient (JRC) before and after shearing (ΔJRC) initially increase and then decrease. In contrast, shear stiffness generally exhibits a decreasing trend, while both residual shear strength and peak shear displacement tend to increase. With prolonged heat treatment, mineral particles undergo thermal expansion and hardening. However, when the number of cycles exceeds five, microcracks within the minerals continue to develop and propagate, leading to further modifications in the mechanical properties of the granite joints. These findings provide valuable insights for assessing the stability of surrounding rock in environments experiencing temperature variations.