The steady performance of spiral-grooved gas film face seal (SGGFFS) is discussed in micro systems. The gas rarefaction effects are considered on sealing performance analysis with two important parameters of Knudsen number (Kn) and accommodation coefficients (ACs). The modified molecular gas lubrication (MMGL) equation is utilized in the analysis of micro gas sealing with considering the gas rarefaction effect. The databases of Poiseuille and Couette flow rate correctors are simultaneously applied in the MMGL equation to expand the lubrication equation with the arbitrary Kn and ACs parameters. Then, the steady-state of MMGL equation is solved by the finite element method to obtain gas pressure distribution. The load capacity is obtained by integrating the pressure distribution of gas film over the sealing face domains. Finally some curves of dimensionless load capacity are depicted for good sealing performance under the operating conditions and gas rarefactions effects.