Abstract: In order to investigate the permeability characteristics in the in-situ crushed coal rock body around the perimeter of gas extraction borehole, the permeability test system of crushed rock body was used to carry out the steady-state permeability test of different grades of crushed coal rock body, and the permeability parameters under different porosity were obtained by controlling the axial displacement and permeability pressure, and the mutual influence relationship between the permeability parameters was analyzed, and the permeability destabilization process was discussed, and the research results showed that the permeability characteristics of crushed coal rock body obey Forchheimer relationship, and with the increase of axial displacement, the permeability resistance of the fluid increases, and the non-Dacry nature of the specimen is more significant. With the decrease of the porosity of the specimen and the increase of Talbol power index, its permeability k decreases and the non-Dacry factor β increases, and the particle fragmentation and transport during the loading of different grades of the specimen will make its internal pore structure adjust and then affect the penetration of the permeability channel. There is a critical characteristic value of seepage instability in the broken coal body, and the expressions for judging seepage instability by permeability and non-Darcy factor are given, and it is found that a negative non-Darcy factor is not a necessary condition for seepage instability, and the critical Reynolds number for seepage instability in the broken coal body is given from the perspective of Reynolds number.