Abstract: The velocity slip calculation method which reflects the rarefied effect was introduced to the Naiver-stokes equation for interpreting the characteristics of aerostatic guideway gas film clearance in micro-scale. The Reynolds equation indicating the flow characteristics of gas film was derived. The pressure distribution of the gas film was simulated. The variation rules of the stiffness of the gas film were calculated with the pressure distribution. This was verified by experiments indirectly and agreeds with the analysis results.