Abstract: During the mining of lower coal seams beneath underground reservoirs, the interlayer rock mass undergoes deformation and failure due to mining-induced disturbances. Crack propagation and interconnection pose significant threat to reservoir safety. Taking the working faces of 2^-2 and 5^-2 coal seams in Shenhua Daliuta Mine as prototypes, this study conducted physical similarity simulation experiments to analyze stress and crack evolution patterns in interlayer rock masses during lower seam extraction. We classified fractures into trace lines and segment lines to investigate the evolution of their topological and geometric characteristics. A three-phase diagram of fractures was established based on average connection numbers to quantitatively evaluate connectivity. Results indicate that as mining advanced, the interlayer rock mass experienced a nonlinear increase in pressure, followed by sudden pressure relief and stress fluctuations. Cracks continued to expand until reaching a maximum aperture before closing. The number of nodes in trace lines and segment lines increased with mining advancement, with the longest trace line typically being a horizontal bedding separation fracture. During evolution, fracture networks predominantly propagated as connected clusters while maintaining spatial continuity. This study provides a method for calculating the safety distance of coal seam mining beneath underground reservoirs and evaluating the safety of interlayer rock masses in coal mines.