Inclusion Criteria:
* Patients must meet the NMOSD diagnostic criteria set by the international NMO Diagnostic Group (IPND) in 2015.
* Serum AQP4-IgG positive.
* Clinical evidence of at least 2 documented relapse (including first attack) in the last 2 years, with at least 1 relapse within 12 months prior to screening.
* Extended Disability Status Scale (EDSS) score ≤7.5 at screening.
* Age 18 to 75 years inclusive, weight at least 35 kg at the time of informed consent.
* If the patients were using the following baseline treatment for relapse prevention, they must be treated at a steady dose for at least 4 weeks prior to enrollment:
* Azathioprine, metecophenol ester and other immunosuppressive agents
* Oral corticosteroid (≦30mg/ day prednisone tablet or equivalent dose of other hormones)
* (patients or their legal representatives) can provide written informed consent indicating that they understand and agree to comply with the requirements of the study protocol.
Exclusion Criteria:
* Continuous treatment with strong or moderate CYP3A inhibitors or inducers is required during the study period. Patients were excluded if they had taken a potent or moderate CYP3A inhibitor or inducer within 7 days prior to administration of the study drug (or had stopped taking these drugs for less than 5 half-lives).
* Previously treated with BTK inhibitors (e.g., ibrutinib).
* Allergic to the study drug or any of the ingredient.
* Desease relaps (including first episode) within the previous 30 days.
* Pregnancy or lactation.
* Previous or current malignancy, except locally recurrent cancers that have received radical treatment (e.g. excised basal or squamous cell skin cancer, cervical or breast cancer in situ).
* Currently central nervous system (CNS) disease that may affect the evaluation of NMOSD.
* Serious and uncontrolled conditions considered by the investigator that could affect safety, compliance and endpoint evaluation, or need for use of a drug not permitted in the protocol.
* Disease that could affected drug absorption, distribution, metabolism, and excretion determined by the investigator.
* Any major clinical infection lead to hospitalization or parenteral antibiotic treatment within 1 month prior to screening; Or other infections that may be aggravated due to the study determined by the investigator.
* Active, latent or undertreated mycobacterium tuberculosis (TB) infection
* Known primary immunodeficiency or underlying disease such as human immunodeficiency virus (HIV) infection.
* Hepatitis B or C virus infection by serological test.
* Received B-cell targeted therapy (e.g. Rituximab) within 6 months prior to the initial administration of the study drug.
* Received biologics such as tozizumab within 12 weeks prior to initial administration of the study drug.
* Received live attenuated vaccine during the screening and study periods, or any live virus vaccine within 8 weeks prior to initial administration.
* Abnormal and clinically significant in ECG examination during screening.
* Uncontrolled hypertension (SBP\>160 mmHg or DBP ≥ 95 mmHg)
* Grade 3 or 4 heart Failure, (NYHA scale).
* Severe liver insufficiency (Child-pugh C).
* Aspartate aminotransferase (AST)\>3 times the upper limit of normal (ULN) and/or alanine aminotransferase (ALT)\>3ULN and/or bilirubin \>2ULN.
* Estimated creatinine clearance \<30 mL/min or requiring dialysis.
* Inability to receive MRI scans
* A history of clinically significant CNS trauma
* Received experimental drug or other experimental treatment within 4 weeks prior to screening or during 5 pharmacokinetic half-lives or duration of biological effects, whichever is longer.
* Participate in another clinical study.
* Accept any of the following:
* BCG vaccination within 1 year prior to screening.
* Prior bone marrow transplant, hematopoietic stem cell transplant, or systemic radiation therapy.
* Received intravenous gamma globulin within 30 days prior to screening.
* Plasmapheresis or leukocyte separation within 90 days prior to screening
* Abnormal white blood cell count, neutrophil count, lymphocyte count, or platelet count during the screening and were considered unsuitable for study by investigator
* Inability to swallow capsules or medical conditions that significantly affect gastrointestinal function
* A history of severe hemorrhagic disorders such as hemophilia A, hemophilia B, von willebrand disease, or a history of spontaneous bleeding requiring blood transfusion or other medical intervention.
* History of stroke or intracranial hemorrhage within 6 months prior to screening
* Current alcohol, drug or chemical abuse, or history of such abuse within 1 year prior to screening.
* Anticoagulants or a combination of anticoagulants and antiplatelet agents is ongoing or planned.
* Any other circumstances in which the investigator or sponsor considers the patient unsuitable for study participation.
