Based on the modern testing technologies and actual measuring data of coalbed methane (CBM) well

using physical and numerical simulation methods

the dynamic variation effect of coal reservoirs permeability during gas recovery has been discussed. The results indicate that permeability has larger difference

which may reach 1-2 order of magnitude; the two opposite regularities of dynamic variation of coal reservoirs permeability are presented between experimental simulation and numerical simulation; that is to say

numerical simulation permeability decreases with the decrease of fluid pressure; while experimental simulation permeability increases with the decrease of fluid pressure. Dynamic characteristics of permeability for two methods seem contradictory; but in fact interrelated. Coal reservoir permeability will be improved gradually during gas recovery. According to comparative analysis

the causes of differences between two methods are revealed. During the whole process

dynamic permeability index should be used to adjust and optimize the work system continuously.