Abstract：Extracting heat from hot dry rock(HDR) and nuclear waste disposal both need researches on granite mechanical characteristics at high temperature and high pressure in depth. Utilizing the 20 MN servo-controlled triaxial rock testing machine with high temperature and pressure developed by the authors，the research of thermal deformation and failure characteristics of large size granite samples of f 200 mm×400 mm at high temperature and triaxial stresses through recent half a year is carried out；and the characteristics of thermo-mechanical parameters such as linear thermal expansion coefficient and elastic modulus changing with temperature，are also achieved. The research results indicate that：(1) Under 3D hydrostatic stress，granite¢s thermal deformation course can be divided into slow deformation stage at low temperature，fast deformation stage at medium-high temperature and slow deformation stage at high temperature. Thermal expansion coefficient measured without stress state may excessively magnify the rock¢s thermal expansion or thermal effect and will result in wrong conclusion，so the thermal expansion coefficient measured with stress state can reflect the actual state of rock mass. (2) Granite shows feature of expansion in volume at low stress while shrinkage in volume after exceeding a certain stress under high temperature and triaxial stresses. It is a different feature contrasted with that of normal temperature. (3) The failure shape of granite at high temperature is of shear failure，while granite will transform to ductility under high confining pressure and high temperature. (4) The elastic modulus of granite decreases with the increase of temperature under confining pressure. The variety course can be divided into three stages，i.e. slow decreasing stage，fast decreasing stage and constant stage.
