Abstract: Based on the random weighted method, the mechanical parameter heterogeneity of each units of the rock mass unit model is achieved. To study the heterogeneous rock mass unit model, the rock bridge transfixion mechanism is analyzed in terms of five main factors: dip angle, rock bridge angle, length, width and end spacing of cracks. Then, a rock bridge transfixion coefficient formula of the surface rock mass under static load is proposed by orthogonal experiment and data fitting, while the existing transfixion coefficient is modified. By adopting the theory proposed above, identification of spatial location of the key block and stability analysis are made using the GeoSMA-3D system in a tunneling project.