When two or more mixed gases pass through a polymer membrane, the relative permeation rates of different gases in the membrane are different due to the difference in solubility and diffusion coefficient of different gases in the membrane. According to this characteristic, under the action of the pressure difference on both sides of the membrane, gases with relatively fast permeation rates such as water, oxygen, carbon dioxide, etc. permeate through the membrane and are enriched on the permeate side of the membrane, while gases with relatively slow permeation rates Gases such as nitrogen, carbon monoxide, argon, etc. are enriched on the stagnation side, so as to achieve the purpose of mixed gas separation. When the pressurized purified air is used as the gas source, inert gases such as nitrogen are enriched into high-purity nitrogen-rich gas, and oxygen-enriched air is evacuated from the permeation side. Compared with the low temperature method and the pressure swing adsorption method, the membrane nitrogen enrichment technology has the advantages of simple operation and continuous and stable work.