Abstarct: The most well-known of these methods for purposes of stability analysis of fractured rock masses is the key-block method (KBM). The KBM only considers key-blocks. If no such blocks are unstable, the method then concludes that the entire rock mass is stable. In reality however, groups of ‘stable’ blocks, when considered as a whole, may in some instances prove unstable. The ‘key-group method (KGM)’ combines groups of collapsible blocks into an iterative and progressive analysis of the stability of discontinuous rock slopes. This method is indeed a 2D limit equilibrium approach. Because the results of 2D analysis are usually conservative, it makes 3D analysis be necessary in huge project. In this project, in order to make a possibility of realest analysis of fractured rock masses, the 2D key group method is developed into three dimensions. Then, using Mathematica software, a computer program was prepared to implement the proposed method on a real case. For validation of proposed method, the implementation results on some assumed model have been compared with outcomes of numerical analysis baxsed on distinction elements by 3DEC software which is used to modeling and analyzing of discontinues areas. For evaluation of reliability of proposed 3D method, its implementation results on real case have been compared with the implementation results of 2D key group method. Tectonic block no.2 of the Choghart open pit mine was investigated as a case study and its geometrical model was created, hence its stability analysis using proposed 3D key group method has been done.