Abstract: According to the complexity about coal deformation and seepage mechanism caused by loading and unloading prccess, the paper used the coupling testi ng equipment of permeability-adsorption-mechanical with coal and transient pulse method, under the condition of 40。C, the penetration behavior of gas in the coal body under different unloading conditions was studied, and the result of experiment of FTIR spectroscopic and transmission electron microscope with unloading raw coal sam ples was comparatively analyzed, the permeability characteristic was affected and its causes the stress effect of microstructure by unloading confining pressure were di scussed from microcosmic.The results showed that the permeability of coal samples overall under-owned with the confining pressure, it rose after unloading, and the eff ective confining pressure was higher, the rate of permeability change was greater.At the micro level, with the increase of confining pressure, the value of spectrum char acteristic parameter 12 increased, aliphatic chain longer and easy to break or fall off, the activity of fissure structure surface enhanced, aliphatic content reduce, coal pa rticles were easy to damage and fracture, these were obviously intensify the micro crack initiation, propagation to form macroscopic crack, at last increased the permea bility of coal body.