Abstract：The relation between seepage and stress is an important problem in numerical analysis of coupled seepage and stress fields of rock mass. The triaxial compressive and seepage experiment of sandstone sample is conducted in the laboratory using triaxial loading apparatus，seepage pressure loading apparatus and medical SOMTOM PLUS CT scanner. By analyzing the experimental results，the porosity equation based on CT numbers is proposed in CT scale. Using the equation，the porosities，real flow rates in porous rock，specific discharge，permeability and the micro-pore diameters during the processes of stress and strain of a sandstone sample are calculated. Results show that the changes of the seepage parameters have closely relations to the processes of damaging and cracking in the sandstone sample. At the first stage of compression test，with the increase of axial compression，the porosity，real flow rate in porous rock，specific discharge，permeability and the micro-pore diameters in a sandstone sample decrease；and the porosity in the sample is closed under compression. After the micro-fracturing initiation in the sample，the porosity，the real flow rate in porous rock，the specific discharge，permeability and the micro-pore diameters increase with the increase of the axial compression. According to the relation between stress and strain of the sandstone sample in macro-scale，the deformation of the sandstone sample is in the elastic deformation stage before the macro-cracking occurrence. At the point of macro-failure，the porosity，the real flow rate in porous rock，the specific discharge，the permeability and the micro-pore diameters reach the maximum values. Meanwhile，it is discovered that the micro-fracture occurs at the elastic deformation stage of rock and the stress of micro-fracturing initiation occupies 45% of the peak strength of the sandstone sample under seepage pressure，but 55% without seepage pressure. This indicates that the strength of the sandstone sample reduces 10% due to seepage pressure.
