Abstract: Based on the principle of pole density statistics，and by applying the three-dimensional statistical method，the space analytic geometry is adopted to directly calculate the included angle.During the statistical process of density，the probability density distribution of the rock mass structural plane in sample space is assumed as normal distribution.According to this spatial distribution，the probability density of each pole is calculated，thus forming a density map with principle and method of the spherical projection.

Key words: ole, Rock mass structural plane, Normal distribution, Probability density, Spherical projection, Density map