Abstract: To investigate the mechanical properties and acoustic emission of thermally damaged sandstone under different temperatures, using MTS815 rock mechanics servo testing machine and acoustic emission to carry out various tests of sandstone at different temperatures(25 °C, 100 °C, 200 °C, 400 °C, 600 °C, 800 °C and 1 000 °C). The results show that the critical temperature of the surface morphology and volume change of sandstone is 400 °C. The temperature of brittle ductile transition of sandstone is 600 °C. The elastic modulus of sandstone increased first and then decreased. On the contrary, the porosity of sandstone decreased first and then increased gradually. From the initial to yield loading stage, the acoustic emission events distributed in a sporadic state. However, the event density of acoustic emission increased sharply from the yielding to the final loading stage. The damage variable defined by the cumulative acoustic emission counts which can better characterize the entire process of damage evolution. Based on the effective medium theory and crack closure model, the theoretical stress-strain curve of sandstone is obtained.