Understanding the thermo-hydro-mechanical processes in various high-temperature/high-pressure underground projects, such as nuclear waste disposal, coal gasification, geothermal energy, and beyond, plays a key role in the assessment and selection of the best and most optimal project sites. Permeability is one of the most important reservoir parameters and is influenced by factors such as stress regime, temperature, rock-mineral composition, and grain size. Within the framework of the AMPEDEK project, the permeability of granites is analyzed under different triaxial stresses, temperatures (30, 60, and 90 °C), and continuous flow. These experiments were conducted using a thermo-triaxial device at the TU Darmstadt laboratory and lasted approximately 12 days each. At 30 and 60 °C, the experimental results show that the permeability changes after one load cycle are small. The initial permeability decreased from 2.72x10-18 to 2.18x10-18 m2 and from 7.36x10-19 to 5.78x10‑19 m2 for 30 and 60 °C, respectively. The experiment at 90 degrees showed a significant and progressive decrease in permeability starting from a mean stress of 10 MPa. The initial permeability decreased from 5.1x10-18 to 4.48x10-20 m2 after 12 days of the experiment. It can be concluded that the coupling effect of high temperature and increased stress has a direct effect on the permeability of the sample. Additionally, two phenomena can be observed during the experiment: 1) the decrease in permeability due to the increase in mean stresses, and 2) the progressive deformation at 90 degrees, and the resulting decrease in permeability, which is amplified by the increase in stresses.