 Aplastic Anemia AA, is a set of bone marrow hematopoietic dysfunction caused by a variety of causes, with hyperplasia of bone marrow hematopoietic cells to reduce whole blood cells and peripheral blood at the characteristics of clinical main performance for anemia, bleeding and infection. According to the severity of the bone marrow failure and the progress of the clinical course ,it is divided into Severe Aplastic Anemia SAA and the Non - Severe Aplastic Anemia NSAA.Severe Aplastic Anemia can be divided into two categories: Very Severe Aplastic Anemia VSAA and Severe Aplastic Anemia SAA, with the characteristics of rapid progress, refractory, poor prognosis, high mortality .The natural course is six months or so, and most patients die in a year . Hematopoietic stem cell transplantation and immunosuppressive therapy are two main treatment . The former is by far the only possible cure. It is recommended as first-line treatments, if patients have a matched sibling donor. The recommended age limit is 40 years old. But for those who have no sibling donor or patients older than 40 years old, it is recommend the immunosuppressive therapy. 