With the development of deep underground engineering, the temperature effect is becoming more and more prominent. Therefore, it is particularly important to study the shear mechanical properties of rock under real-time high-temperature conditions (25 ~ 280 ℃). Using a novel multifunctional true triaxial shear apparatus for rocks developed by Northeastern University, the direct shear tests and true triaxial shear tests of intact gray sandstone under real-time high-temperature conditions were carried out. The study revealed the influence of normal stress, lateral stress, and temperature on the peak shear strength, shear stiffness, and failure mode of sandstone. The test results indicate that both normal stress and lateral stress can enhance the peak shear strength of gray sandstone, and the impact of temperature varies depending on the normal stress. Increasing the lateral stress and normal stress can improve the shear stiffness, while an increase in temperature can inhibit this enhancement. The presence of lateral stress hinders the increase in lateral deformation during shearing and reduces the lateral spalling of rock blocks.