Abstract: Coalbed methane compressibility factor is necessary to calculate the free gas in coal reservoir. The data of coalbed methane compressibility factor is usually obtained by checking methane compression factor table, however, this method is not so accurate. In order to establish an analytical calculation model for coalbed methane compressibility factor, which is suitable for conditions of the composition of coalbed methane and the temperature and pressure of coal reservoir, REFPROP 8.0 sofware is used to calculate the methane compressibility factor at temperature of 0~100℃ and pressure of 0~30 MPa. An analytical calculation model for pure methane compressibility factor is established with reduced temperature and reduced pressure as independent variables. Based on this model, an analytical calculation model for coalbed methane compressibility factor is established by means of corresponding states principle and weighted processing approach. The calculated result from this model shows that the relative error is less than 2.5%, with an average value of 1.48%. This model can be used to calculate free gas content in coal reservoir