Abstract: Regulatory T cells（Treg） play a dominant role in selftolerance and control of autoimmune diseases. These cells also play a pivotal role in chronic inflammation and cancer by limiting immune activation and specific immune response. The study shows Treg can be divided into two subsets including natural（n） Treg and inducible（i） Treg. Natural（n） Treg is normally responsible for maintaining peripheral tolerance and immune balance in healthy individuals. Inducible（i） Treg is highly suppressive， therapy-resistant Treg which down-regulate anti-tumor immune responses and promote tumor growth. But this division of labor between nTreg and iTreg is not absolute， and overlap may be common. This review is aim to discuss the phenotypic diversity and plasticity of the Treg， and then investigate the relationship between Treg and tumor prognosis and immunity therapy.