The purpose of this study is to evaluate the efficacy and safety of iguratimod compared to placebo in patients with active primary Sjogren's Syndrome.

Inclusion Criteria:

• meet the 2016 American College of Rheumatology (ACR) / European League Against Rheumatism Classification Criteria for Sjogren's Syndrome (EULAR SS)
• ESSDAI score ≥6
• IgG >16 g/L
• Positive anti-SS-A/Ro antibody at screening

Exclusion Criteria:

• Pregnancy or breast feeding

• Secondary Sjogren's syndrome

• severe renal or haematological failure, a history of cancer, hepatitis B or C, human immunodeficiency virus, severe diabetes or any other chronic disease or evidence of infection

• Prior administration of any of the following:

  1. Rituximab in the past 12 months prior to randomization;
  2. Cyclophosphamide, mycophenolate mofetil, methotrexate, leflunomide and iguratimod in the past 12 weeks prior to randomization;
  3. Azathioprine, cyclosporin, tacrolimus, sirolimus, sulfasalazine in the past 4 weeks prior to randomization;
  4. live vaccine in the past 12 weeks prior to randomization

• Corticosteroids: > 10 mg/day oral prednisone (or equivalent); Any change or initiation of new dose within 4 weeks prior to randomization; Intramuscular, subcutaneous, intravenous, or intra-articular corticosteroids within 4 weeks prior to randomization.