Inclusion Criteria:
* Able to comprehend the research study and voluntarily signing the informed consent form (ICF).
* Renal biopsy report supporting diagnosis of primary IgAN within 8 years prior to the screening visit.
* Estimated Glomerular Filtration Rate (eGFR) (using the Chronic Kidney Disease Epidemiology Collaboration formula) ≥ 30 mL/min/1.73 (m\*m) at screening and baseline.
* Prior to the baseline visit, all subjects must have received standard care treatment, including good blood pressure control and a stable treatment of a maximum recommended or maximum tolerated dose of angiotensin-converting enzyme inhibitors(ACEI) or Angiotensin receptor blocker(ARB) for at least 12 weeks.
* 24-hour urinary protein-to-creatinine ratio (24h-UPCR) ≥ 0.75 g/g or 24-hour urinary protein excretion (24h-UPE) ≥ 1 g/d during the screening and baseline periods.
Exclusion Criteria:
* Secondary IgAN judged by the investigator: Secondary IgAN may be associated with Henoch-Schonlein purpura, hepatic cirrhosis, coeliac disease, human immunodeficiency virus (HIV) infection, dermatitis herpetiformis, seronegative arthritis, small cell carcinoma, lymphoma, disseminated tuberculosis, obliterative bronchiolitis, inflammatory bowel disease, familial Mediterranean fever, etc.
* Known allergy to monoclonal antibody drugs or to the excipients of CM313.
* Presence of rapidly progressive glomerulonephritis (RPGN), defined as 50% decline in eGFR within 3 months prior to randomization and/or crescent formation in more than 50% of glomeruli in a renal pathological specimen.
* Confirmed acute kidney injury (AKI) within 4 weeks prior to randomization.
* Vaccination of any live vaccine within 30 days prior to dosing or planned vaccination during the study period.
* History of transplantation (any solid organ transplant, including renal transplant, bone marrow transplant, etc.) or plan to undergo renal transplantation during the study.
* History of severe recurrent or chronic infection.
* Malignant tumor within 5 years prior to screening (except for completely cured cervix carcinoma in situ and non-skin squamous cell carcinoma metastatic or basal cell carcinoma).
