Abstract: In order to investigate the impact of different low-pressure points on a,b measured values,through high-pressure volumetric method and isothermal desorption experiments of coal samples from different mines,according to the adsorption,pressure and temperature met the Langmuir equation under high pressure,a and b values were calculated by using the least square method.comprehensive analysis showed that different set of different low-voltage points resulted in the different of a,b measured values.Adsorption will be obtained by substituting pressure points that measured the same into Langmuir equation.It was obtained by comparing with the actual adsorption capacity of this pressure that the adsorption calculated from a and b values was relatively small to the measured values when low voltage point was 0.6 to 1.1 MPa.Similarly,the pressure calculated from same adsorption had the same conclusion.