Black seaweed extract is mostly prepared by chemical extraction method (such as alkali depyretic extraction) or physical crushing + biochemical extraction process. Among them, the alkali depyretic extraction process is simple to operate. Seaweed polysaccharides are degraded into small molecular substances by adding alkali solution and hydrolyzing them at 60-90 ℃ for 3-12 hours. However, high temperature will inactivate more than 30% of auxin active substances and may produce macromolecular precipitation. The physical crushing method breaks algae by means of high-pressure grinding and the like to avoid chemical addition at low temperature in the whole process and reduce the loss of active ingredients, but the extraction efficiency is low, nutrient release is inadequate. Some high-quality products are combined with subsequent processes such as adsorption concentration and film drying to improve product purity and solubility, and the moisture content of the dried solid product is usually less than 5%.