The goal of this clinical trial is to find the best dose of zanubrutinib when used together with high-dose dexamethasone for adults who are newly diagnosed with primary immune thrombocytopenia (ITP), and to learn how safe and effective this combination treatment is.

Inclusion Criteria:

1. Confirmed newly-diagnosed, treatment-naive ITP;
2. Platelet counts <30×10^9/L ;
3. Platelet counts < 50×10^9/L and significant bleeding symptoms (WHO bleeding scale 2 or above);
4. Willing and able to sign written informed consent.

Exclusion Criteria:

1. Received chemotherapy or anticoagulants or other drugs affecting the platelet counts within 6 months before the screening visit;
2. Received first-line and second-line ITP-specific treatments (eg, steriods, cyclophosphamide, 6-mercaptopurine, vincristine, vinblastine, etc) ;
3. Current HIV infection or hepatitis B virus or hepatitis C virus infections;
4. Active infection;
5. Maligancy;
6. Severe medical condition (lung, hepatic or renal disorder) other than ITP. Unstable or uncontrolled disease or condition related to or impacting cardiac function (e.g., unstable angina, congestive heart failure, uncontrolled hypertension or cardiac arrhythmia);
7. Female patients who are nursing or pregnant, who may be pregnant, or who contemplate pregnancy during the study period; a history of clinically significant adverse reactions to previous corticosteroid therapy
8. Have a known diagnosis of other autoimmune diseases, established in the medical history and laboratory findings with positive results for the determination of antinuclear antibodies, anti-cardiolipin antibodies, lupus anticoagulant or direct Coombs test;
9. Patients who are deemed unsuitable for the study by the investigator.