Inclusion Criteria:  Males and females > 18 years old and <75 years old (non-pregnant, non-lactating females). Patients fulfilled the Berlin diagnostic criteria of acute respiratory distress syndrome, with a arterial oxygen partial pressure (PaO2) to fraction of inspired oxygen (FiO2) between 150 mmHg and 300 mmHg. Signed written informed consent has been obtained  Exclusion Criteria:  History of chronic respiratory disease Single cardiogenic pulmonary edema Apach2 score ≥21 points Complicated with end-stage disease, or poor prognosis judged by the clinical doctor in charge ARDS course>3 days Agranulocytosis or receiving immunosuppressive agents or high doses of corticosteroids (methylprednisolone>40mg/day) Pregnancy or breastfeeding Participated in this study Do not agree to participate in this experiment