Abstract：Orientation distribution of rock mass joints has been studied by scholars for about four decades，but the features of joint orientation distribution are still not easy to be described，because the orientation is distributed in the bivariate manner；and it is difficult to be used in the rock engineering. The method to combine the idea of box-counting method by Benoit Mandelbrot with the skill of lower hemisphere Schmidt equal area polar plot and the dynamic box-counting method by a computer program is employed to study the features of joint orientation distribution for each cluster. Then the fractal dimension of discontinuities pole on the lower hemisphere Schmidt equal area polar plot is calculated；and the basic regulations of orientation distribution and the relation between the fractal dimension and orientation dispersivity are put forward. The basic regulations of the fractal dimension of the joint orientation pole are that the more poles of the orientation clusters are，the higher value of the fractal dimension is. However，the results are not always the cases；and the fractal dimension values will be different when the values of the orientation ranges are different，even for the same amounts of poles of the cluster orientation. It shows that the higher fractal dimension of the orientation cluster is，the wider range of the orientation value for the cluster is，i.e. the more dispersivity is shown for the cluster orientation.
