Abstract: In order to investigate the difference of the pore distribution in the coal reservoirs with high and low rank coal affected to the coal bed methane enrichme nt and the penetration migration,according to the pressurized mercury and balanced water isothermal adsorption experiment results of the high and low rank coal sampl es,the paper analyzed the pore development features of the high and low rank coal and compared the difference of the pore volume fractals in the high and low rank co al.The results showed that low porosity of the high rank coal, small content of the influent pore,inkstand type semi-sealed pore development would cause a connection r eduction of the pore,a poor influent capacity,a high micro pore content,a low moisture content and a high adsorption capacity and would be favorable to the enrichment of coal bed methane.The porosity of low rank coal would be large.The specific pore volume of the large,medium and transition pore all would be large,the connection of the pores would be good and the influent capacity would be high. The small specific surface area and high moisture content would cause the adsorption capacity reduce d.The coal bed methane development of high rank coal reservoir should improve permeability and coal bed methane development of low rank coal reservoir should be fi rst to select methane enrichment zone.