Abstract: In the sealing section of double-prevention boreholes along the coal seam, the coal mass is characterized by a significant presence of pores and fracture structures, forming seepage channels through which air from the roadway infiltrates the extraction boreholes, thereby affecting the gas extraction efficiency. Based on the structural characteristics of the coal mass in the sealing section of double-prevention boreholes, a self-developed triaxial permeability testing platform for coal was utilized to design and conduct permeability experiments on coal samples with combined pore-fracture structures. The experiments measured and calculated parameters such as porosity, gas seepage velocity, pressure gradient, permeability, and effective stress during the permeability process. The influence of effective stress on coal permeability was analyzed, and the permeability behavior of coal in the sealing section of double-prevention boreholes was explored. The results indicate that: Under the action of stress, the skeletal structure within the fractured coal sample undergoes deformation, with internal particles experiencing dislocation and further fracturing. This reduces the number of gas seepage channels, leading to a decrease in permeability. As the load continues to increase, the coal structure becomes relatively compacted and densified, and the sensitivity of permeability to changes in porosity diminishes, gradually stabilizing. The pressure gradient shows a significant decreasing trend with increasing seepage velocity. At low seepage velocities, the relationship between the two exhibits a clear Darcy phenomenon. At higher velocities, the seepage velocity-pressure gradient curve gradually deviates from linearity, conforming to the Forchheimer relationship. Gas flow in the sealing section of double-prevention boreholes is partitioned between the fractured zone and the broken zone of the coal mass. When gas flows through coal with a single pore size, it creeps along the surface of the coal particles, and changes in the structure of the seepage channels have a relatively small impact on resistance. However, at the transition interface of coal with dual-combination pore sizes, abrupt changes occur in the pore structure of the coal mass. During the gas permeation process, the flow velocity is redistributed, generating additional inertial resistance and causing significant fluctuations in nonlinear laminar flow. Effective stress can effectively characterize the inhibitory effect on seepage velocity. As effective stress increases, sliding between fractured coal particles and deformation or breakage of the particles themselves may occur, resulting in continuous compaction and densification of the skeletal structure. This leads to the closure of pore seepage channels and a linear decrease in gas seepage velocity. A pore-throat expansion-contraction model was developed to theoretically analyze the relationship between effective stress and seepage velocity, with experimental results aligning well with theoretical predictions. Effective stress is the key factor causing changes in coal permeability. The permeability k of the sample decreases with increasing effective stress σ_e. At the interface of dual-pore-size combined coal media, significant differences in pore structure result in pronounced nonlinear fluctuations in gas flow. These fluctuations also lead to greater variations in coal permeability with changes in effective stress. The above research indicates that the degree of coal fragmentation during gas migration can characterize the permeability properties of the coal seam, serving as a basis for quantifying the structural parameters of the coal in the sealing section of double-prevention boreholes. This provides important theoretical guidance for optimizing borehole arrangement and grouting parameters in the sealing section of double-prevention boreholes along the coal seam.