 Liver failure LF is a dramatic clinical syndrome with massive necrosis of liver cells. Although liver transplantation provides an option to cure patients suffering with LF, lack of donors, postoperative complications, especially rejection, and high cost limit its application. Previous study showed that bone marrow derived mesenchymal stem cells BM-MSCs the novel and promising therapeutic strategy, BM-MSCs can replace hepatocytes in injured liver, and effectively rescue experimental liver failure and contribute to liver regeneration. Plasma exchange PE can improve internal environment by removing endotoxin, it helps the liver regeneration and functional recovery and make UC-MSC differentiation into hepatocyte like cells, and exert immunomodulatory function. In this study, safety and efficacy of human umbilical cord mesenchymal stem cells UC-MSCs transplantation combined with plasma exchange PE for patients with liver failure caused by hepatitis B Virus will be evaluated. 