Abstract: The common shale clay (illite and kaolinite) equilibrated in different relative (RH) humidity environment in advance are collected to conduct the N2 adsorption / desorption and high-pressure methane sorption isotherms test. Furthermore,the pore size distribution with different water contents is analyzed,and the water saturation with various RH is quantitated with the view of pore volume and its influence on clay adsorption capacity is also studied. The results indicate that the pore characteristics considering the water content vary significantly comparing with the dry condition. The fine pores less than 5． 15 nm will disappear on the pore size distribution curves because of the capillary condensa- tion effect at the RH of 98% ,and the significant decrease of specific surface area is also accompanied. It can be also concluded that the water adsorption for clay mineral depends on the fine pores,the Sw for kaolinite is 71. 43% and higher than the value of 46. 15% for illite while the RH is 98% due to the richer micropores of the former. In this con- dition,the adsorption capacity decreases by 85% which is caused by the blocked effect of condensed water and the change of adsorption mechanism (methane adsorbed on the water film rather than the pore wall). However,the experi- ments in dry condition mainly overstated the methane adsorption contribution of fine pores and cannot represent the ac- tual shale reservoir characteristics.