Abstract: The coalbed methane is in an undersaturated state under the initial reservoir condition. There exists the critical desorption in coalbed methane production. According to the production performance, it is demonstrated that the coalbed methane adsorption does not conform to gas?solid adsorption regulation. The gas?solid adsorption must be saturated, and cannot have the critical desorption process. The liquid phase adsorption theory of coalbed methane can not only solve the critical desorption problem, but also satisfy the situation of coalbed methane generation. Due to the difference of molecule polar, the liquid phase adsorption volume is larger than the gas phase adsorption. Meanwhile, the undersaturated solution state of coalbed methane in water leads to critical desorption phenomenon. The coalbed methane critical desorption pressure has no relation with liquid phase adsorption coefficient, and it is calculated by the solubility of coalbed methane in water and the volume fraction of coalbed methane in water in reservoir conditions