Interleukin-33 (IL-33), as a member of the interleukin-1 (IL-1) family, is an endogenous cytokine released by damaged or necrotic barrier cells (endothelial cells and epithelial cells). IL-33 signal transduction depends on the recognition and interaction of specific receptor growth stimulating gene 2 protein (ST2), which is mainly expressed in immune cells. IL-33 regulates type 2 immune response by targeting Th2 cells, mast cells, eosinophils, type 2 innate lymphoid cells (ILC2), and type 1 immune response through CD8+T, NK, and DCs cells. Recent studies have shown that IL-33/ST2 signal transduction affects peripheral dynamic balance, phenotypic diversity, and function of regulatory T cells (Treg). Since Treg is necessary to establish and maintain immune tolerance, it is of great significance to study the role of IL-33/ST2 signal in Treg biology for the treatment of immune diseases. This review discusses the different effects of IL-33/ST2 signal on Treg, to provide reference for the diagnosis and treatment of cancer, inflammation, and autoimmune diseases.