This is a multicenter, double-blind, randomized, placebo-controlled, loaded Phase III clinical study. This test is in a new coronavirus infection pneumonia diagnosis and treatment plan of 9 (trial version) "(SoC), on the basis of the standard treatments according to the results of clinical studies have been obtained, using a dose of 0.2 mg/kg, and a placebo. The regimen consisted of a single intravenous infusion of Meplazumab or placebo on day 1 (d0) of the treatment period and d7 after initial administration at a dose of 0.2 mg/kg calculated according to body weight. It is expected that 350 subjects will be randomly assigned to Meplazumab or placebo in a 1:1 ratio. Short-term efficacy evaluation was performed for each subject within 28 days after initial administration to determine the therapeutic efficacy and safety of Meplazumab. Long-term follow-up evaluation was performed within 56 days of initial administration to determine the safety of Meplazumab in each subject.

Inclusion Criteria:

1. Age ≥18 years old, male or female;
2. Patients with clinically confirmed 2019-ncov infection (severe) in accordance with the National Health Commission's "Diagnosis and Treatment Protocol for novel coronavirus Infection (Trial version 10)";;
3. Agree to use a highly effective non-pharmacologic contraceptive method within 3 months after signing ICF to the end of the trial;
4. Subjects must be able to understand the study and willing to participate in the study, and sign an informed consent form (if the researcher believes that it is in the interests of the subjects to participate in the study, the informed consent form should be signed by the legal guardian of the subjects and explained in the original medical records and other relevant documents).

Exclusion Criteria:

1. Any physical examination results, laboratory abnormalities and/or any medical history of the subject may, in the investigator's judgment, endanger the subject's safety by participating in the study;
2. Use of an anti-coronavirus treatment such as Paxlovid (nematavir/ritonavir combination package) within 3 half-lives before the first dose or during the study period, About 6.05 h at t1/2), Azvudine tablets (about 9 h at t1/2), and monolavir capsules (about 3.3 h at t1/2) h), ambavirumab/romisivir injection (t1/2 about 45 days /75 days), COVID-19 human immunoglobulin (t1/2 about 3-4 weeks) or recovery plasma (t1/2 about 21 days), deuremidvir hydrobromide tablets (t1/2 about 4.80-6.95 hours), senotevir tablets/ritonavir tablets The combination package (t1/2 about 4.14 h), baritinib (t1/2 about 12.5 h), tocilizumab (t1/2 about 21.5 days), remdesivir (t1/2 about 27 h), lenreterivir (t1/2 about 14.9 h), favelavir (t1/2 about 4.5 h) h), 2-deoxy-D-glucose (t1/2 about 50 min), etc.
3. Critically ill patients with clinically confirmed 2019-ncov infection according to the Diagnosis and Treatment Protocol for 2019 novel Coronavirus Infection (Trial version 10) issued by the National Health Commission of the People's Republic of China;
4. Stage 4 severe chronic kidney disease requiring dialysis (i.e., estimated glomerular filtration rate [eGFR] < 30 mL/min/1.73 m2), an increase in serum creatinine of 44.2 μmol/L within 7 days, oliguria (< 400 mL/24 hours) or anuria (< 100 mL/24 hours);
5. During pregnancy or lactation;
6. They will be transferred to another hospital other than the study site within 72 hours;
7. Known to be allergic to the test drug and its components;
8. No live vaccine (live attenuated vaccine) was administered within 2 weeks before randomization or during study treatment and safety follow-up;
9. Subjects participating in another clinical study at the same time. A washout period of 5 half-lives is required (depending on the study drug or 30 days from any previous study, whichever is longer);
10. Total bilirubin (TBL) > 2× upper limit of normal (ULN), alanine aminotransferase (ALT) > 5×ULN, aspartate aminotransferase (AST) > 5×ULN, or alkaline phosphatase > 5×ULN;
11. Platelet count < 50×109/L or hemoglobin < 70 g/L;
12. Other factors that the investigator deemed inappropriate for trial entry.

Note: researchers should ensure that participants when screening meets all inclusion/exclusion standard. If a subject's status changes (including laboratory results) between screening and initial dosing and if the subject meets one of the exclusion criteria, the subject shall be excluded from the study.