inclusion criteria: 1. aged 18-65 years; 2. voluntarily participate in this clinical trial and sign off "informed consent form"; 3. diagnosed with severe pneumonia of covid: respiratory distress, rr \>30 times / min; resting oxygen saturation of 93% or less; arterial partial pressure of oxygen / oxygen concentration 300mmhg; sars-cov-2 nucleic acid test was positive. 4. chest imaging confirm covid-19 featured lesions in lung.

inclusion criteria: 1. aged 18-65 years; 2. voluntarily participate in this clinical trial and sign off "informed consent form"; 3. diagnosed with severe pneumonia of covid: respiratory distress, rr \>30 times / min; resting oxygen saturation of 93% or less; arterial partial pressure of oxygen / oxygen concentration 300mmhg; sars-cov-2 nucleic acid test was positive. 4. chest imaging confirm covid-19 featured lesions in lung.

inclusion criteria: aged 18-65 years; voluntarily participate in this clinical trial and sign off "informed consent form"; diagnosed with severe pneumonia of covid: respiratory distress, rr >30 times / min; resting oxygen saturation of 93% or less; arterial partial pressure of oxygen / oxygen concentration 300mmhg; sars-cov-2 nucleic acid test was positive. chest imaging confirm covid-19 featured lesions in lung.

inclusion criteria: aged 18-65 years; voluntarily participate in this clinical trial and sign off "informed consent form"; diagnosed with severe pneumonia of covid: respiratory distress, rr >30 times / min; resting oxygen saturation of 93% or less; arterial partial pressure of oxygen / oxygen concentration 300mmhg; sars-cov-2 nucleic acid test was positive. chest imaging confirm covid-19 featured lesions in lung.

inclusion criteria: 1. aged 18-65 years; 2. voluntarily participate in this clinical trial and sign off "informed consent form"; 3. diagnosed with severe pneumonia of covid: respiratory distress, rr >30 times / min; resting oxygen saturation of 93% or less; arterial partial pressure of oxygen / oxygen concentration 300mmhg; sars-cov-2 nucleic acid test was positive. 4. chest imaging confirm covid-19 featured lesions in lung.

inclusion criteria: 1. aged 18-65 years; 2. voluntarily participate in this clinical trial and sign off "informed consent form"; 3. diagnosed with severe pneumonia of covid: respiratory distress, rr >30 times / min; resting oxygen saturation of 93% or less; arterial partial pressure of oxygen / oxygen concentration 300mmhg; sars-cov-2 nucleic acid test was positive. 4. chest imaging confirm covid-19 featured lesions in lung.