inclusion criteria: * the age ranges from 18 to 75 (inclusive), regardless of gender. * patients diagnosed with severe and critical covid-19 pneumonia within one week, according to the chinese diagnostic criteria for covid-19 pneumonia in the diagnosis and treatment plan for covid-19 pneumonia (tentative ninth edition). * 20kg/m2≤body mass index（bmi）≤30 kg/m2. * volunteer to participate in this clinical study and sign the written informed consent.

inclusion criteria: * the age ranges from 18 to 75 (inclusive), regardless of gender. * patients diagnosed with severe and critical covid-19 pneumonia within one week, according to the chinese diagnostic criteria for covid-19 pneumonia in the diagnosis and treatment plan for covid-19 pneumonia (tentative ninth edition). * 20kg/m2≤body mass index（bmi）≤30 kg/m2. * volunteer to participate in this clinical study and sign the written informed consent.

inclusion criteria: the age ranges from 18 to 75 (inclusive), regardless of gender. patients diagnosed with severe and critical covid-19 pneumonia within one week, according to the chinese diagnostic criteria for covid-19 pneumonia in the diagnosis and treatment plan for covid-19 pneumonia (tentative ninth edition). 20kg/m2≤body mass index（bmi）≤30 kg/m2. volunteer to participate in this clinical study and sign the written informed consent.

inclusion criteria: the age ranges from 18 to 75 (inclusive), regardless of gender. patients diagnosed with severe and critical covid-19 pneumonia within one week, according to the chinese diagnostic criteria for covid-19 pneumonia in the diagnosis and treatment plan for covid-19 pneumonia (tentative ninth edition). 20kg/m2≤body mass index（bmi）≤30 kg/m2. volunteer to participate in this clinical study and sign the written informed consent.