Abstract: The meso-failure progress of sandstone under temperatureeffects was observed and studied in-situ through Scanning Electron Microscopy(SEM). The SEM observations under thermal-mechanical coupling effects showedthe brittle fracture on the different places, independent bearing mineralsand the bifurcated cracks in the sandstone sample. The numer of microcracksor the branch cracks near the main crack was large below the temperature of100°C and small over 150°C. Within the temperature from25°C to 300°C, the fracture toughness of sandstone increased firstly and thendecreased. There was the threshold temperature of 150°C forsandstone at meso-scale. With the rising temperature, the failutre ofsandstone will obtain the transition from brittle to ductile behavior.Sandstone failure modes were experimental observed, such as transgranular,intergranular and mixed mode. Meanwhile, the deformation field of sandstonewas measured using digital speckle correlation method (DSCM).