With the rapid development of industry, Industrial Nitrogen Generators have been widely applied in chemical industry, electronics, metallurgy, food, machinery and other fields, among which PSA nitrogen making machine using pressure swing adsorption technology has become the mainstream nitrogen making method, in which carbon molecular sieve is the key material to determine the production capacity of nitrogen making machine. Because the compressed air provided by air compressor usually contains trace amounts of oil, water and dust particles, these impurities, especially oil molecules, will reduce the adsorption capacity of carbon molecular sieve, so the compressed air must remove oil and water dust before entering the oxygen and nitrogen separation system. First of all, the air is compressed to 0.75-1.0MPa by the compressor into the air purification system, by the pipeline filter to remove most of the water, oil and dust impurities, and then by the freezing dryer cooling water pressure dew point reached 2℃-10℃, again through the fine filter, super fine filter filtration, activated carbon oil remover, Clean compressed air with pressure of 0.75mpa to 1.0MPa, pressure dew point of 2℃ to 10℃ and oil content ≤0.01PPm is obtained. The compressed air purification system consists of pipeline filter, freeze dryer, fine filter, super fine filter, activated carbon oil remover, automatic blowdown valve, ball valve and so on.