Based on the experiments of liquidsolid adsorption, the uneven pore structure in coal has been found. The pore size of mediumhigh rank coal mainly ranges from 0.8 nm to 1.5 nm. The surface curvature of the pore varies apparently. The variety of the pore size can be indicated by Weibull asymmetry fuction, with which liquidsolid adsorption equation can be derived. Based on the adsorptiondesorption isotherm experiments of No. 3 Jinchengshi River Coal Mine, No. 3 Xiangshan Coal Mine in Ancheng and No. 43 Liudaowan Coal Mine in Xinjiang, and the data are fitted by SPSS, so if r generally exceeds the fitting effects of Langmuir equation, the guidance of CBM production can be facilitated.