Recurrent spontaneous abortion (RSA) has various causes, including chromosomal abnormalities, a prethrombotic state, and abnormal uterine anatomical factors. However, in about 50% of cases, the cause remains unknown and is referred to as unexplained recurrent spontaneous abortion (URSA). The fetus is protected from rejection by the maternal system, acting as an allogeneic gene, and immune tolerance serves as a crucial mechanism. The Th17/Treg cell paradigm's emergence as a new subpopulation of CD4 T cells, interacting with one another, plays an essential role in the immune microenvironment and the body's defense system. This Th17/Treg cell model helps to explain the pathology of recurrent miscarriage that could not be accounted for by the original immune mechanism based on the Th1/Th2 model. Furthermore, the plasticity of Th17 and Treg cells holds innovative significance in autoimmunity and abortion. This paper reviews the role of Th17/Treg cellular immune response in the maintaining normal pregnancy and understanding unexplained recurrent spontaneous abortion.