Abstract: With the decrease of gas pressure in cleat, changes occur in the absolute permeability of coal-bed methane (CBM) reservoirs during primary depletion. To investigate this variation,based on the volumetric balance among the factors of bulk coal, solid grains and pores, how the MATCHSTICK strain changes with pore pressure is studied in this paper first. Furthermore, how permeability varies with the strain changes is researched and then the regularity of permeability changes is proposed. The rationality of applying MATCHSTICK strain changes to analyze permeability is proved by the curves of strain and permeability changes obtained from production field and laboratory.