Inclusion Criteria:
1. Male or female subjects with the age of ≥18 and ≤ 65 years old at the time of informed consent.
2. Able to understand the procedures and methods of this study, and will to provide a signed and dated informed consent form.
3. Diagnosed alopecia areata(AA) without other reasons caused alopecia.
4. Have severe AA, as determined by all of the following:Current AA episode of more than 6 months' duration and hair loss encompassing ≥50% of the scalp, including alopecia totalis (AT) and alopecia universalis (AU);No spontaneous improvement over the past 6 months;Current episode of severe AA of less than 8 years.
5. All women of childbearing potential and all men must be willing to use at least one highly effective method of contraception from the signing of informed consent, throughout the duration of the study, and for 3 months after the last dose of investigational drugs.
Exclusion Criteria:
1. Known history of anaphylaxis to any of the ingredients and/or other similar products.
2. Participated in a clinical trial of any drug or medical device and has used an investigational product (including placebo and control group) or treatment within 1 month or 5 half-lives before randomization.
3. Previously treated with JAK inhibitors.
4. Corticosteroids, finasteride, minoxidil,topical immunotherapy treated within 8 weeks before randomization.
5. Diphenylcyclopropenone (DPCP), HMGCoA reductase inhibitor, Chinese herbal medicine treated within 4 weeks before randomization.
6. With other diseases: acute "diffuse" type of AA, lymphoproliferative disease, tumor, severe chronic gastrointestinal disease, thyroid disorders, serious cardiovascular disease.
7. Subjects with evidence of clinical laboratory abnormalities at screening that, in the opinion of the investigator, may affect the safety of subjects or the interpretation of study results: Hemoglobin level \< 10.0 g/dL. Absolute white blood cell (WBC) count /absolute neutrophil count (NEUT)/absolute lymphocyte count(LYMPH)\<LLN. Aspartate aminotransferase (AST), or alanine aminotransferase (ALT) \> 2 × ULN, total bilirubin(TBIL)\>1.5 × ULN. QTcF\> 450ms. Subjects with eGFR ≤ 60 mL/min based on Cockcroft-Gault calculation.
8. The subject had or currently has a severe infection, and had a severe infection judged by the investigator within 1 month before randomization: HBV, TP-Ab, HIV, HCV, TB positive.
9. Subjects who are unsuitable to the trial, as identified by the investigator.
