Supercritical carbon dioxide extraction technology is a new separation technology developed in recent years. It is called "green separation technology" because of its advantages such as safety, energy saving, non-toxic, harmless, no residual solvent, reusable solvent, low operating temperature, strong selectivity, and non-flammability. It is more suitable for the separation and purification of physiologically active substances and natural products, and has become an effective means of separating products in the fields of medicine, food, environmental protection, flavors and fragrances. 1. Basic principles and characteristics of supercritical extraction technology Supercritical fluid mainly refers to fluids above critical pressure and critical temperature, with unique physical and chemical properties, and has the advantages of both liquid and gas; its viscosity is small, which is close to gas; its density is high, which is close to liquid. The diffusion coefficient is dozens or even hundreds of times larger than that of liquid. Therefore, supercritical fluid has strong solubility, good transmission and fluidity, and its pressure and temperature changes are more sensitive near the critical point. CO2 is more commonly used in actual industrial production. Its advantages are: non-toxic, low processing temperature, strong selectivity, non-flammable, safe, energy-saving, and reusable solvents. It is more suitable for the food industry and pharmaceutical industry; the critical temperature is relatively low, the products are easy to separate, and there is no solvent residue, which is more suitable for the separation of thermally unstable substances; the critical pressure is relatively moderate, and it is convenient to transport; the chemical properties are inactive, non-flammable, generally do not react with other substances, and the operation is safe.