Abstract: Traditional graphic analysis is inadequate and greatly influenced by subjective experience. A new method based on firefly algorithm is proposed to partition the discontinuity orientation data. The sine of the acute angle between the unit normal vector of two discontinuities is used to quantify the distance between the orientation of these discontinuities. Then， the fuzzy objective function is established and firefly algorithm is chosen to search the optimal clustering centers. At the same time， the boundaries between different sets are determined. Since the firefly algorithm has the outstanding ability of global optimization and a fast convergence speed， the new algorithm has the advantages of time saving and high efficiency. Finally， this new method is applied in discontinuity orientation data partition at Songta dam site， Nujiang River. The results indicate that the new approach is reasonable and has obvious superiority.

Key words: rock mechanics, structural plane, attitude data partition, clustering method, firefly algorithm