Allo-geneic stem cell transplantation(allo-HSCT) cure thalassemia major by destroying the original hematopoietic and immune systems with a large dose of chemotherapy, rebuilding a new system to correct the abnormal hematopoietic globin chain synthesis which leads to hemolysis. Currently, it is the only curative means. According to donors, allo-HSCT could be sibling allogeneic hematopoietic stem cell transplantation and unrelated allogeneic hematopoietic stem cell transplantation(URD-HSCT). URD-HSCT could expand the range of treatment among β-thalassemia major patients. As recently reported , 68 cases of thalassemia patients at the median age of 15 (2 to 37 ) received unrelated donor BMT. According to Pesaro rating classification, 14 patients were attributed to type Ⅰ, 16 cases Ⅱ type , 38 cases type III, overall survival and thalassemia free survival rates were 79.3% and 65.8%. A survey among 59 evaluable patients indicated that grade Ⅱ ~ Ⅳ aGVHD occurred in 24 cases (40%) , in which 10 cases (17%) were grade Ⅲ ~ Ⅳ aGVHD. Similar results were seen in other reports, 21 patients received unrelated donor BMT, with a 2-year thalassemia free survival rate of 71%. GVHD happened in 3 cases, and 3 patients died. Our institution has conducted a total of 10 cases of URD-HSCT to treat severe thalassemia, using methotrexate + cyclosporine A+ mycophenolate mofetil to prevent graft-versus-host disease, 9 cases of disease-free survival, 1 case with graft rejection. Incidence of Ⅲ-Ⅳ severe acute graft-versus-host disease (aGVHD) was 20%. Severe aGVHD incidence was 20%. Our research group has found there is a high risk to develop aGVHD, especially severe aGVHD for heavy thalassemia patients who receive URD-HSCT, which seriously affects the prognosis and survival, while increasing medical costs and the financial burden on the patients' families.