Galactooligosaccharide (GOS) is a non-artificial oligosaccharide derived from animal milk. In nature, there is a small amount of galacto-oligosaccharide in animal milk, while human breast milk contains more. It has the general characteristics of oligosaccharides and has good bifidobacteria proliferation activity. It is a high-quality prebiotic. Galactooligosaccharides (GOS) is a kind of functional oligosaccharides with natural properties. Its molecular structure is generally connected with 1-7 galactose groups on galactose or glucose molecules. In nature, there is a trace amount of GOS in animal milk, while human breast milk contains a large amount. The establishment of the bifidobacteria flora in infants largely depends on the GOS components in breast milk.