Study to Evaluate the Safety and Efficacy ofJaktinib Hydrochloride Tablets in Severe Alopecia Areata

Inclusion Criteria: * 18 years age or older ,male or female； * Alopecia areata diagnosed clinically； * Patients with alopecia accounting for 50% or more of the total scalp area and stable for at least 6 months or more； * Patients can complete treatment for at least six months； * Requirements for pregnant or lactating female and male and female of childbearing age；Female patients must be satisfied：Menopause (defined as no menstruation for at least one year);Or have been surgically sterilized；Or have fertility, but must satisfy：Pregnancy tests conducted within 7 days before randomization must be negative；And agree to use appropriate contraceptive methods throughout the trial period, including at least one barrier method；And no breastfeeding；Male patients must agree to use appropriate contraceptive measures throughout the trial, including at least one barrier method； * Patients are voluntarily enrolled in the Study and can be treated and visited according to the requirements of the protocol after signing the Informed Consent Form； Exclusion Criteria: * Alopecia caused by syphilitic alopecia, thyroid disease, trichotilomania, head moss, connective tissue disease, infection, zinc deficiency and iron deficiency; * Patients with acute diffuse alopecia areata (ADTAFS) * Patients with active tuberculosis * The following diseases were combined within 6 months before randomization:thyroid diseases ，liver diseases, malnutrition, heart diseases, nervous system diseases, gastrointestinal disorders, tumors and psychiatric diseases * HIV positive, active hepatitis B virus positive (HBsAg or HBeAg positive) and HCV-RNA positive at screening； * Other patients with abnormal history or clinical manifestations that may affect participants participation in the study or may confuse the results of the study； * Within two weeks before randomization，Patients who received glucocorticoid topical therapy, anthracene ointment, minoxidil, SADBE/DPCP contact immunotherapy, photochemotherapy or cryotherapy； * Before randomization，oral or injected any medicines to treat hair loss (including the glucocorticoids was detected in injection, systemic corticosteroids, antihistamines, stephania drugs, glycyrrhizin, glycine, methionine compound tablet, compound glycyrrhizin glucoside) and other liquorice extract, ring spore element, anti TNF antibody, IFN - gamma, IL - 2 antibodies, for alopecia areata therapy of traditional Chinese medicine and other JAK inhibitor) and washout period less than seven half-life of patients; * Participants in a clinical trial of any drug or medical device within 4 weeks prior to randomization.