The principle of nitrogen generator of air separation unit is based on the principle of pressure swing adsorption. High quality carbon molecular sieve is used as adsorbent to produce nitrogen from air under certain pressure. After purification and drying of compressed air, pressure adsorption and decompression desorption were carried out in the adsorber. Due to the kinetic effect, the diffusion rate of oxygen in carbon molecular sieve micropores is much higher than that of nitrogen. When the adsorption does not reach equilibrium, nitrogen is enriched in the gas phase to form finished nitrogen.