Much attention should be paid to the permeability of broken rocks in goafs for the sake of water preservation in mining and to prevent disasters. Using a special device together with the MTS815.02 Rock Mechanics Test System, we tested the permeability of broken mudstone during its compacting process, and obtained the relations between axial stress and differential seepage pressure and between the pressure gradient and the seepage velocity. The effect of axial stress, grain size, and seepage velocities on the permeability coefficient is analyzed. The results show that 1) permability varies abruptly when the load reaches the compressive strength of rock samples, 2) for a constant seepage velocity, the differential seepage pressure and the axial stress can be expressed by an exponential function, 3) for a constant axial stress, the pressure gradient and the seepage velocity can be also expressed by an exponential function and 4) the permeability coefficient of broken mudstone of different sizes is closely related to its compaction state and will decrease with the increase of axial stress, expressed as a logarithmic function.