The analysis of dominant orientations of discontinuities is a basic work for a further study on simulating with Monte-Carlo method and conforming the stability of rock mass. Traditional analysis of plots method is insufficient and inadequate. The result is only a simply classification of the orientations

and is inconvenient to be applied in practice. Because of the deficiency of traditional analysis method

a dynamic clustering algorithm is developed. According to the rule of right hand

a three-dimensional field coordinate system is constructed. A unit normal can be used to represent the orientation of discontinuity. Then the orientations are classified by the dots' spherical distance. A data investigated from a slope in the new town of Badong County in the Three Gorges Reservoir is used to be a case study. The study shows that the results of dynamic cluster algorithm are reliable and reasonable. And the dominant orientations and classification are more precision.