Umbilical cord blood hematopoietic stem cells have the advantages of rapid acquisition, convenient source, no harm to the donor, low requirement for HLA matching, low incidence and mild degree of graft-versus-host disease (GVHD), and no decline in the effect of graft-versus-leukemia (GVL), etc., and have become one of the important sources of hematopoietic stem cells. Research at the University of Minnesota shows that for patients in urgent need of transplantation, 54% of those who successfully find umbilical cord blood and 21% of those who find bone marrow within 1 year; the average time to obtain bone marrow is 49 days, while the umbilical cord blood is 13.5 days; therefore, the search for umbilical cord blood stem cells is more rapid and easier to obtain than bone marrow banking stem cells. It is especially appropriate for those who need a transplant urgently. The immune cells in cord blood hematopoietic stem cells are mostly naive, immature immune cells, so the incidence and severity of graft-versus-host disease (GVHD) after unrelated cord blood transplants are significantly reduced compared with unrelated bone marrow transplants (the incidence of III-IV GVHD is only half of that of bone marrow transplants), which not only reduces the number of transplantation failures due to GVHD but also avoids the need for complicated GVHD prevention and treatment techniques. This not only reduces graft failure due to GVHD, but also avoids a series of comorbidities and high costs associated with complex GVHD prevention and treatment techniques. Cord blood stem cell transplantation also plays an important role in GVL because of the abundance of CD16-CD56+ NK cells in umbilical cord blood and the amount of CD3+ T cells in the same amount as in bone marrow. Therefore, cord blood stem cells are a reasonable alternative for patients without a suitable bone marrow donor. Especially for pediatric patients, double cord blood transplantation can be chosen for adults. 1995 Laporte JP et al. first used cord blood stem cell transplantation for adult patients with success, pioneering the use of UCBT in adults. Margaret L et al. reported that transplantation using double HLA incompatible cord blood hematopoietic stem cells as a donor source resulted in a higher incidence of second-degree aGVHD, but the patients’ 1-year graft-related risk was higher. higher, but patients had a lower 1-year transplant-related mortality (TRM). Bipartite cord blood transplantation is being performed more and more widely in adult hematologic diseases, providing another important source of stem cells for adult stem cell transplantation. Indications: (1) A variety of malignant neoplastic diseases: various types of leukemia, myelodysplastic syndromes, malignant lymphoma, multiple myeloma, breast cancer, ovarian cancer, neuroblastoma, and small cell lung cancer. For some tumor patients, hematopoietic stem cell transplantation is the only radical cure, such as refractory or relapsed acute leukemia, chronic myeloid leukemia, myelodysplastic syndromes, and so on. (2) Bone marrow failure due to multiple causes: severe aplastic anemia, severe hematopoietic stem cell damage due to radiation or drugs. Due to the lack of or severe damage to the patient’s hematopoietic stem cells, the patient is unable to produce a sufficient amount of blood cells, and the patient often dies due to bleeding and infection. (3) Hereditary blood and immune system diseases: such as hereditary severe combined immunodeficiency disease, thalassemia, hemoglobinopathies, glucose encephalopathy (Gaucher’s disease), and neurophospholipidosis (Niemann’s disease). (4) Various autoimmune diseases: In recent years, hematopoietic stem cell transplantation has been found to be able to treat a variety of serious and refractory autoimmune diseases, such as systemic lupus erythematosus, systemic sclerosis, and so on. Umbilical cord blood stem cell transplantation is especially suitable for acute leukemia, severe aplastic anemia, severe radiation sickness, where the patient needs urgent transplantation treatment, but there is no sibling donor, and no compatible unrelated donor can be found in the bone marrow bank in the short term.