The purpose of this study is to initially observe the safety and effectivity of RC18 in Participants with Primary Sjögren's Syndrome.

Inclusion Criteria:

• Voluntarily signed informed consent ;
• Patient with primary Sjögren's syndrome according to the European - American consensus group criteria.
• Seropositive at screening for anti-Ro/Sjögren's syndrome type A(SSA) antibodies
• ESSDAI score ≥ 5.

Exclusion Criteria:

• Diagnosis of secondary Sjogren's syndrome, such as rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis and other autoimmune diseases;
• Abnormal laboratory parameters need to be excluded, including but not limited to:
• Immunosuppressive agents were used within 4 weeks prior to randomization.;
• The use of hydroxychloroquine was allowed during the trial, and the pre-randomized drug regimen was stable for less than 12 weeks;
• Use of biological agents for targeted therapy in the first 6 months of randomization;
• Treatment of primary Sjogren's syndrome with traditional Chinese medicine and proprietary Chinese medicine within 4 weeks before randomization;
• The use of saliva-stimulating drugs within 7 days prior to randomization;
• Sodium hyaluronate eye drops, artificial tears can be used, and the stability time of the randomized pre-medication scheme is less than 4 weeks;
• Intravenous immunoglobulin therapy or plasma exchange therapy within 6 months before randomization;
• Infection with herpes zoster or HIV and hepatitis C virus(HCV) antibody positive;
• Currently suffering from active hepatitis or severe liver lesions and history;
• Malignant tumor patients ;
• Combined with involvement of important organs or neuropathy;
• Have participated in any clinical trial in the first 28 days of the initial screening or 5 times half-life period of the study compound (taking the time for the shorter).
• Pregnant , lactating women and men or women who have birth plans during the research;
• Investigator considers candidates not appropriating for the study