Abstract: It is confirmed at first that the volume correction should be conducted in the adsorbance calculation during the isothermal adsorption measurement,and the former volume correction method is discussed.It is considered that the application of former equation has a certain test condition,and the real adsorbance could be extracted by the direct method and indirect method,respectively.Taking the volume of adsorbed phase as the considering object and directly putting into the equation,the direct method utilizes the mass conservation law,and extract the real sdsorbed increment ΔV_s;the indirect method still follows the former correction method,but the apparent adsorbed increment is revised at first and obtained ΔV_a,then the ΔV_s is extracted using the former correction method.At the same time,it is indicated that the correction method is based on both assumptions:(1)the coal volume is invariable with the adsorption process;(2)the density of adsorbed phase is a constant.