Abstract: Human milk oligosaccharides (HMOs) are very important components in human milk, and more than 200 different HMOs have been identified so far. HMOs act as prebiotics by the metabolism of gut microbiota to produce short-chain fatty acids, which have a beneficial effect on infant health. This is one of the main differences between breast milk and formula milk powder. Studies have shown that different species of gut microbiota use different mechanisms to recognize and digest HMOs with different structures, maintaining the balance of the gut microbiota. HMOs also have a variety of functions such as relieving allergic symptoms and preventing necrotizing enterocolitis. In this paper, the type, structure and content of HMOs, interaction between HMOs and infant gut microbiota, and their immune regulatory functions are reviewed. HMOs can promote colonization and growth of gut microbiota in infants, and directly or indirectly regulate the infant immune function. This paper provides theoretical support for the application of HMOs in infant foods, and contributes new ideas to the future research and development direction.