Abstract:Rock mass mechanics and seepage characteristics of the high level radioactive waste disposal candidate site—Beishan,Gansu Province,are studied with field joint survey,geostress test,high-pressure hydraulic test and rock mechanic test in laboratory. The study indicates that the most of rock mass joints in Beishan,Gansu Province,are with shear joint with steep angle of inclination. Distribution of joint¢s inclination direction can be effectively fitted by normal function,and the distribution of joint¢s aperture can be effectively fitted by negative exponential function. Rock of Beishan,Gansu Province,is of high density,low water content,low permeability,and low porosity. Rock near the ground and tonalite is not uniform,and the granite 300 meters below the ground is uniform with uniaxial compression strength and Young¢s module. The maximum principal horizontal stress is 17.52 MPa,and the minor principal horizontal stress is 11.12 MPa,which show that it is under a moderate geostress site. The coefficient of permeability of rock mass is about 10-7–10-5 cm/s with a low permeability. Codes of permeability tensor calculation and 3D joint simulation are programmed,where the seepage characteristic and 3D joint distribution can be visualized.