Abstract: Rock permeability is one of important research contents of rock mechanics, especially in the process of deep energy development, permeability characteristic after thermal damage is closely related to the stability and safety of rock engineering. In order to study flow law of fluid inside thermal damaged rock, the permeability coefficient of thermal damaged rock is analyzed as confining pressure gradient increased step by step from 10 MPa to 30 MPa, aiming at the yellow sandstone samples treated at five different temperatures（100 ℃, 200 ℃, 400 ℃, 600 ℃, 800 ℃）. The pore distribution characteristics of rock at different temperatures are revealed and the correlation between the microstructure and permeability characteristics is established. The test results show that: ①high temperature induces the volume flow velocity inside the rock to be significantly higher than that at normal temperature and lower temperature. Therefore, the permeability coefficient of thermal damaged yellow sandstone increases with the increase of heat treatment temperature under the same confining pressure, and the permeability coefficient of sandstone treats at 800℃ can increase by 50 times. ②Confining pressure can narrow the seepage channel inside the rock and increase the resistance of fluid migration. The permeability coefficient shows a change relationship with the power function of confining pressure, but the influence of confining pressure on permeability coefficient is different under different temperatures. ③Thermal damage can change the pore structure of yellow sandstone and increase the number of micro-cracks and pores. However, the pore size distribution characteristics of yellow sandstone samples caused by different high temperatures are different, showing that with the increase of temperature, the pore size distribution fluctuation increases and the proportion of large-scale pore size increases. ④The fractal dimension of pores in thermal damaged yellow sandstone show an increasing trend with increasing temperature, and the fitting relation between the fractal dimension of pores and permeability coefficient is good under different confining pressures, indicating that the change in rock permeability coefficient with temperature is essentially due to the change in pore structure caused by rock thermal damage.