Abstract: It is the basis to study the changing law for coal crack fissure in the process of mining and digging by finding out the laws of permeability of coal petrography under different loading and unloading paths. With RMT-150B rock mechanics test system, the permeability tests of conventional tri-axial and loading-unloading of different coal samples were tested in different stress and different deformation steps. The variation of permeability was summarized based on the evolution mechanism of pore fissured, and the mechanism of change was analyzed. The results showed that when loading and unloading was before the peak, permeability was changed in a lesser extent; the lag of strain-permeability curve was not obvious, compared with stress-strain curve. The variation mainly depended on the elastic deformation. When loading and unloading was after the peak, the permeability was changed absolutely, and increased by a big amplitude. At the same time, the lag of strain-permeability curve was very obvious, comparing with stress-strain curve, the variation mainly depended on the plastic deformation. At the same time, with the increases of cyclic loading and unloading times, the permeability became larger by degree. In particular, in the same process of loading and unloading, the difference of permeability between the loading and unloading in the sane strain was great.