Abstract: In order to study the gas permeability of coal gangue backfilling body, based on the pressure- difference method and Darcy's law, an experimental system for measuring the gas permeability has been proposed. And a series of experiments under various particle gradation，different surrounding rock pressures and different gas concentration have been conducted by using the system. The results have shown that the gas permeability coefficients of coal gangue backfilling body measured by the experiment are in the interval of [0.649，3.206] m2/(MPa2·d)，which belong to the appropriate scope of gas drainage，and that the coal gangue backfilling body has good air penetrability. Based on the results of the experiments, the paper has put forward various methods such as appropriate increase of the grain size of coal gangue backfilling body and the ventilation quantity between working face ends, and decrease of the bearing capacity of coal gangue backfilling body and the gas concentration of packing area to increase the gas permeability of coal gangue backfilling body, and the experimental results have provided theoretical guidance for safe and highly effective gangue backfilling technology development under the circumstance of protective layer mining.

Key words: coal gangue backfilling body, different particle gradation, different surrounding rock pressure, different concentration of gas, gas permeability coefficient