This study is an Investigator initiated, randomized, multicenter, double-blind, placebo-control study. The aim of this study is to evaluate the safety and efficiency of Sirolimus for primaty antiphospholipid syndrome patients at week 24 and week 48.

Inclusion Criteria:

1. Understand and sign the informed consent form
2. Male or Female
3. aged 18-70 at the time of screening visit
4. Met 2006 Sapporo classification criteria of APS or 2023 ACR/EULAR classification criteria of APS
5. With the stable combination therapy

Exclusion Criteria:

1. history of serious adverse events or contraindication to Sirolimus
2. Catastrophic APS within 90 days
3. Acute thrombosis within 30 days
4. ≥4/11 American College of Rheumatology Classification Criteria for SLE or other systemic autoimmune diseases
5. Historically positive HIV test or test positive at screening for HIV
6. currently on any suppressive therapy for a chronic infection (such as tuberculosis, hepatitis B infection, hepatitis C infection, CMV, EBV, Syphilis, etc)
7. Surgery treatment within one month
8. History of malignant neoplasm within the last 5 years
9. White blood cell counts<3×10*9/L
10. Abnormal Liver function tests: ALT or AST ≥ 1.5 times the upper limit of the normal value, and total bilirubin and blood lipids ≥ 2 times the upper limit of the normal value
11. Pregnant or pregnancy preparation or breastfeed
12. Any circumstances that may cause the subjects to be unable to complete the study or pose significant risks to the subjects