This study will evaluate the efficacy, safety, pharmacokinetics(PK), pharmacodynamics(PD) and ADA of MIL62 compared with placebo in participants with systemic lupus erythematosus.

Inclusion Criteria:

1. Age 18-80 ;
2. Diagnosis of systemic lupus erythematosus according to European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) SLE classification criteria ;
3. Positive antinuclear antibodies (ANA) ≥ 1:80 at screening or positive anti- dsDNA ;
4. Low C3 and/or low C4 complement at screening ;
5. High disease activity at screening ;
6. On a stable SLE treatment regimen for at least 30 days prior to the first administration；
7. Able and willing to provide written informed consent and to comply with the study protocol.

Exclusion Criteria:

1. Unsufficient organ function;
2. Received rituximab or any B-cell depleting drug within 9 months prior to the first dose;
3. Subjects with CD4+ T lymphocyte count < 200 cells/μL;
4. Received cyclophosphamide within 8 weeks prior to the first dose; received calcineurin inhibitors (cyclosporine, tacrolimus, etc., except for topical use) or plasma exchange therapy within 4 weeks prior to the first dose;
5. Received a B-cell stimulating factor inhibitor such as Belimumab, and Telitacicept within 12 weeks prior to the first administration; TNF inhibitor, interleukin monoclonal antibody, JAK inhibitor, BTK inhibitor, TYK2 inhibitor, or thalidomide within 4 weeks prior to the first administration;
6. Received live or attenuated vaccination within 28 days prior to the first administration;
7. Participated in other clinical trials within 28 days prior to the first administration;
8. Concomitant with other serious diseases;
9. Positive for hepatitis B surface antigen (HBsAg) and/or hepatitis B core antibody (HBcAb) with HBV DNA titer above the normal range; positive for hepatitis C virus (HCV) antibody; positive for human immunodeficiency virus (HIV);
10. Subjects with known history of severe allergic reactions to humanized monoclonal antibodies MIL62 ;
11. Breastfeeding or pregnant women;
12. Childbearing potential and unwillingness or impossibility to comply with a scientifically acceptable birth-control method;
13. Other conditions unsuitable for participation in this study determined by the Investigator.