The air-to-air vacuum sealing device is composed of evacuated multi stages and the differential pumping system to maintain the pressure of the deposition chamber at 5 x 10(-2) Pa. The differential pumping system is adopted to evacuate the deposition chamber with minimum power consumption and pumps cost through the estimation of air flow rate and pressure. The air flow rate of each stage (Q) and pressure (P) is calculated accurately in region of viscos flow, viscos slip flow, transient flow. molecular flow based on the experimental results.