Abstract: Based on triaxial permeability test system, the strength characteristics and permeability evolution law of coal-rock specimens of different height ratios of rock to coal under the condition of simulating different thicknesses of roof-coal-floor are studied. The results show that the peak strength values for coal-rock specimens are different due to the different height ratios of rock to coal, and the peak stress increases with the height ratio. The broken and failure models of the coal-rock combination specimens show a macroscopic shear fracture surface, and the fracture surface runs through the top and bottom rocks. With the increase of the axial strain, the permeability evolution law of the coal-rock combination specimen shows the “V” shape, which decreases to the lowest point first and then increases rapidly. And the corresponding axial strain of the permeability curve increases with the increase of the height ratio of rock to coal.