Abstract: Based on Euclidean distance, the hierarchical cluster method was adopted to analyze the unit normal vectors converted from the dip angle and dip direction of Bayan Obo East Iron Mine on the premise that the rectangular coordinates system was construc-ted. A proper distribution model was chosen to describe each joint group, and its validity was verified by chi-square test. It is found that the hierarchical cluster method can analyze the joint attitude accurately and provide reasonable classification of joint attitude without any uncertainty caused by human judgment. Based on the hierarchical cluster result of rock mass joints and slope design parameters, the most probable slope instability mode is determined by the stereographic horizon projection technique, which provides a basis for ad-justing slope design parameters and controlling slope disaster.