Hetrombopag for Pediatric Patients With Chronic Immune Thrombocytopenia

Inclusion Criteria: 1. Age ≥ 6 years old and ≤ 17 years old,both sexes. 2. Part A:Confirmed diagnosis of ITP ≥6months; Part B: Confirmed diagnosis of ITP ≥12months;Platelets \<30×10\^9/L twice in a row,and platelets \<30×10\^9/L before taking the medicine. 3. Subjects who are refractory or have relapsed after at least one prior ITP therapy. 4. Birth control during and 28 days after the trial. 5. Written informed consent must be obtained from the patient's guardian and accompanying informed assent from the patient (for children over 8 years old). Exclusion Criteria: 1. No evidence of other causes of thrombocytopenia. 2. Diagnosis as Evans or Wiskott-Aldrich comprehensive. 3. Patients with any prior history of arterial or venous thrombosis, or diagnosis as thrombophilia. 4. Suffering from serious, progressive, uncontrolled kidney, liver, gastrointestinal, endocrine, lung, heart, nervous system, brain, or mental illness. 5. ALT, AST, or ALP\> 1.5 x upper limit of normal (ULN), DBLI, or Scr \> 1.2 x upper limit of normal (ULN). 6. Active HIV or HCV-Ab positive,HBsAg positive. 7. PT result exceeds normal by more than ±3s, APTT result exceeds normal by more than ±10s 8. Participated in clinical trials of other drugs (received experimental drugs) within 3 months prior to medication. 9. The inestigators determined that other conditions were inappropriate for participation in this clinical trial.