Under the low vacuum condition formed by the operation of the pre-vacuum pump, the silicone oil in the pump is heated to be boiled by heat to generate steam, which is ejected at a very high speed through the gaps of the nozzles of the pump to diffuse the gas molecules inside the container. It is brought to the position of the pre-stage vacuum pump in the steam, and is quickly extracted by the pre-stage vacuum pump to make the system reach the high vacuum requirement.