When the effect of real gas in the calculation of micro gap gas lubrication is considered,the molecule mean free path of the real gas is required to calculate.A calculation method of the molecule mean free path of the real gas was proposed based on Virial coefficient.According to this calculation method,the compressibility factor in real gas state equation was determined by Virial equation,and by substituting the ideal gas state equation with the real gas state equation,the molecule mean free path of the real gas was calculated based on the algorithm of the molecule mean free path of the ideal gas.The molecule mean free paths of the real gas of dry air,CO2,N2,H2 at different pressures were calculated respectively by using this method,and compared with the results of their ideal gas. The results show that the molecule mean free paths of the real gas of dry air are quit close to the calculation results from the idea gas.Under normal pressure,the molecule mean free paths of the real gas of the dry air,CO2,N2 are slightly less than those of their ideal gas,and the molecule mean free path of the real gas of H2 is slightly larger than that of the ideal gas.Along the increasing of the pressure,the molecule mean free path is decreased;and the difference of the molecule mean free path between the real gas and the ideal gas is increased.