Abstract: A lot of pores and fractures in some coal reservoirs are blocked by minerals or impurities,such as calcite and dolomite. The permeability of those coal seams is low. This paper puts forward a new method to increase permea-bility by acidification. In order to study the law of meso-structure of coal under the action of acidification,those param-eters,such as specific surface area,pore volume,porosity,permeability,pore size distribution and magnetic resonance imaging,are measured by low temperature nitrogen adsorption and NMR experiments. Test results show that the coal samples’saturated water state NMR signal increases,irreducible water state NMR signal cut down,and the changes about mid-large pores peak (T2 >20 ms) is much bigger than small pores peak in T2 spectrum. The parameters that quantified by NMR,such as total porosity,effective porosity,and permeability were increased,and the residual porosity and T2 cut-off values were decreased. The specific surface area and total pore volume were increased,which quantified by the low temperature nitrogen adsorption,and the increase was mainly concentrated at the pore size of 10 nm,but the increase of high rank coal was not obvious. The nuclear magnetic resonance image directly reflects the change charac-teristics of the internal pore structure before and after the coal sample acidification,which provides a new way to reveal the microscopic evolution law of acidification. The comparison shows that the initial porosity of coal sample is more de-veloped or more carbonate,silicate and other soluble minerals in the pore,the greater the change of the characteristic parameters,the better the effect of acidification.