Hepatopulmonary syndrome (HPS) is defined as a triad of liver disease and/or portal hypertension, intrapulmonary vascular dilatations (IPVD) and increased alveolar-arterial oxygen gradient that causes a severe hypoxemia. Obviously, the pathological hallmark of HPS is IPVD.IPVD, an event that causes elevated arteriovenous shunts and ventilation-perfusion mismatch,increase pulmonary blood flow and cardiac output. In addition, compared to normal settings,oxygen molecules must traverse longer distance to bind to hemoglobin in erythrocytes in condition of enlarged alveolar capillary diameter, which leads to incomplete oxygen equilibration within erythrocytes exiting the pulmonary capillaries. Some studies also suggest that pulmonary angiogenesis participates in the pathogenesis of HPS. What's more, HPS occasionally accompanies with portopulmonary hypertension (PoPH), which further aggravates hypoxemia.HPS markedly decrease the life quality and increases the mortality of patients. Although HPS has been researched for nearly 30 years, until now, no clearly effective medical therapy for HPS is available except liver transplantation (LT).