This study is divided into two parts (Part A and Part B). This study aims to evaluate the safety and efficacy of CM313 in subjects with primary Immunoglobulin A nephropathy(IgAN), while also observing its Pharmacokinetics(PK) characteristics, Pharmacokinetics(PD) effects, and immunogenicity.

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).