Four evolution patterns of rock permeability in damage process are summarized. And how rock pore

micro cracks and lithology form the four patterns of rock permeability evolution is analyzed. The impact of confining pressure on permeability is also presented. The permeability reduces along with the increase of confining pressure before rock failure

however， it is complex after rock failure

and it is necessary to do further research. Statistical analysis is carried out to analyze the variation range of permeability in the process of damage

which shows soft rocks vary less while hard rocks vary more. In the experiments in which the confining pressure is between 1 MPa to 40 MPa

permeability variation of 85.9% rock is within 100 times

97% within 1000 times. Furthermore

the difference between instability of seepage and that of structure under the function of seepage is distinguished. It is proposed that the presence or absence of non-Darcy flow should be considered from the point of effective stress law.