Based on the field geology survey data, the probability distribution function of joint aperture was analyzed and the availability of the fitting data was verified. The joint aperture data observed the previous fitted function can be generated in the process of joint simulation. The seepage of rock mass is proportional to the third power of joint’s aperture. It is much more reasonable and feasible to analyze the permeability tensor of rock mass with the previous generated data. At the same time, the method comprehensively considered the effect of joint’s orientation, aperture, scale and their distribution.