Abstract: Milk serves as a crucial source of nutrition and immune protection for newborns. Its proteins exhibit a holistic mechanism of action: rather than functioning in isolation, they assemble into complexes through mutual interactions. These complexes demonstrate superior efficacy in nutrient delivery and immune protection compared to their isolated counterparts. This paper reviews advances in understanding the interaction mechanisms of milk-derived proteins, encompassing forms such as charge interaction, domain-specific binding, and cofactor-mediated association. It further examines the immunoregulatory effects of these protein complexes, including direct antimicrobial activities, regulation of immune cell function and inflammatory responses, enhancement of intestinal barrier integrity and flora balance, and promotion of immune system maturation. The analysis of current research challenges and future directions provides a new perspective for developing novel functional foods and immunomodulators.