Laboratory confirmed COVID-19 by PCR Aged 18 to 70 years old Being inpatients The clinical severe or immediately life-threatening COVID-19 (Severe patients meet any of the following: Dyspnea, Respiratory frequency ≥ 30/min, Blood oxygen saturation ≤ 93% (in resting state), partial pressure of arterial oxygen to fraction of inspired oxygen ratio (PaO2/FiO2)<300, and/or Lung infiltrates > 50% within 24 to 48 hours. Life-threatening disease is defined as: respiratory failure and need mechanical ventilation, septic shock, and/or multiple organ dysfunction or failure The patient or his/her legal guardian will sign the informed consent and participate voluntarily Accepting randomized allocation (allocating into any group) Being hospitalized before the end of the clinical trial and available for any follow-up

Laboratory confirmed COVID-19 by PCR Aged 18 to 70 years old Being inpatients The clinical severe or immediately life-threatening COVID-19 (Severe patients meet any of the following: Dyspnea, Respiratory frequency ≥ 30/min, Blood oxygen saturation ≤ 93% (in resting state), partial pressure of arterial oxygen to fraction of inspired oxygen ratio (PaO2/FiO2)<300, and/or Lung infiltrates > 50% within 24 to 48 hours. Life-threatening disease is defined as: respiratory failure and need mechanical ventilation, septic shock, and/or multiple organ dysfunction or failure The patient or his/her legal guardian will sign the informed consent and participate voluntarily Accepting randomized allocation (allocating into any group) Being hospitalized before the end of the clinical trial and available for any follow-up