Abstract: According to the poor permeability and low recovery rate of the coalbed methane reservoir in China,a self made triaxial permeameter was applied to the permeability experiment on CO2 under both conventional and supercritical conditions.Based on the experiment of the macropermeabilityimprovement a micro image experiment was conducted. The fractal theory.image processing,Matlab programming and other data processing method were applied to pick up the micro pore features of the coal samples after the permeability improved and to calculate the surfaceporosity.The box dimension analysis picture and the pore distribution fractal dimension were obtained.The development degree of the coal microstructure after the CO2 functioned was quantitatively analyzed.The macro permeability improved experiment results showed that afer the supercritical CO2 functioned,the permeability was increased by over ten times than the conventional CO2 and the ous.The micro image results showed that the coal porosity distrbution had obvious features.After the superoritical CO2 functioned ,the fractal dimension of the coal pore distribution and the surface porosity were both higher than the coal samples after the conventional CO2 functioned.The pore distribution quantitative calculation results were the same to the results of the scanning electron microseope.T he micro experiment results showed that the supereritical CO2 could effectively promote the development of the coal micro pore.T'he micro and macro experiments combined showed that the supercritical Co2 would have excellent role to improve the permeability of the low permeable seam.