• Maximum plasma concentration (Cmax) [ Time Frame: Day 15, 16, 29, 43 and 47 ]
  Maximum plasma concentration (Cmax)
• Area under the concentration-time curve in a selected time interval (AUC0-t) [ Time Frame: Day 15, 16, 29, 43 and 47 ]
  Area under the concentration-time curve in a selected time interval (AUC0-t)
• Rate of Clinical Remission [ Time Frame: Day 1 to 8 weeks treatment ]
  Rate of Clinical Remission was defined as the proportion of patients with two consecutive visits in the first 8 weeks (including the 8th week) during the medication period, platelet count ≥30×10^9/L, and a 2-fold increase from baseline (no emergency treatment during the period)

• Maximum plasma concentration (Cmax) [ Time Frame: Day 15, 16, 29, 43 and 47 in dose esclation phase and Day 15, 29, 43 and 57 in dose expansion phase ]
  Maximum plasma concentration (Cmax)
• Area under the concentration-time curve in a selected time interval (AUC0-t) [ Time Frame: Day 15, 16, 29, 43 and 47 in dose esclation phase and Day 15, 29, 43 and 57 in dose expansion phase ]
  Area under the concentration-time curve in a selected time interval (AUC0-t)
• Clinical remission rate [ Time Frame: 1st dose to 8 weeks treatment ]
  Clinical remission rate defined as the proportion of patients who have PLT ≥30×10^9/L and increased ≥20×10^9/L vs baseline without anti-ITP emergency treatment during the study

• Drug: HMPL-523
  HMPL-523 will be oral administrated once daily for 8 weeks and 16 weeks open-label treatment.
• Drug: Placebo
  HMPL-523 matching placebo will be oral administrated once daily for 8 weeks and 16 weeks open-label treatment.

• Active Comparator: treatment arm
  Eligible subjects will be treated with planned dose of 100 mg, 200 mg and 300 mg HMPL-523 once daily for 8 weeks and 16 weeks open-label treatment.
  Intervention: Drug: HMPL-523
• Placebo Comparator: placebo arm
  Eligible subjects will be treated with HMPL-523 matching placebo once daily for 8 weeks and 16 weeks open-label treatment.
  Interventions:

  • Drug: HMPL-523
  • Drug: Placebo

Inclusion Criteria:

1. Signed informed consent form
2. 18~75 years old male of female
3. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
4. Diagnosed immune thrombocytopenia before randomization with platelet decrease for more than 6 months.
5. Patients with refractory or relapsed ITP who have been treated with 1st line anti-ITP regimen or have experienced splenectomy.
6. Relative stable disease with World Health Organization (WHO) bleeding score of 0-1 and no rescue treatment needed within 2 weeks based on investigator's judgment.

7. Laboratory tests meet the following conditions：

   • During screening stage, twice PLT<30x10^9/L(exceed 24 hours)
   • Hb≥90g/L(if iron-deficiency anemia,Hb>80g/L),WBC>2.5x10^9/L, NEU>1.8x10^9/L
   • Crea≤1.5xULN and CCR≥50mL/min
   • TBIL、ALT、AST≤1.5xULN
   • Amylase、lipase<ULN
   • INR、APTT<20%xULN

Exclusion Criteria:

1. Patients with secondary thrombocytopenia or patients have other auto immune diseases who need long term steroids or immunosuppressants treatment.
2. Patients with Myelofibrosis, Myelodysplastic syndrome, Aplastic anemia, or other hematologic malignancies.
3. Have splenectomy within 12 weeks before randomization
4. Major surgery was performed within 4 weeks before randomization;Or require major elective surgery during the study period.
5. Have malignant tumor(except basal cell carcinoma of skin and carcinoma in situ of cervix)
6. Have previous/significant arterial/venous embolic disease
7. History of serious cardiovascular disease, or QTc≥450 ms.
8. Patients with resistant hypertension (Systolic blood pressure ≥140 mmHg or Diastolic blood pressure ≥90 mmHg)
9. Has a history of severe gastrointestinal diseases, such as dysphagia, active gastric ulcer, and is unable to take oral medication or has absorption disorder
10. HIV infection
11. Uncontrolled, active infections
12. Known history of clinically significant liver disease, such as hepatitis b（HBV DNA ≥2000IU/mL (or ≥1×104 copies)）, hepatitis c, or cirrhosis
13. Prior anti-ITP emergency treatment within 2 weeks before randomization.
14. Prior anti-ITP treatment within 4 weeks before randomization except for stable dose steroids, including but not limited to Thrombopoietin, thrombopoietin receptor agonist, azathioprine, cyclosporine A and mycophenolate mofetil.
15. Any condition requiring anti-coagulant therapy or the regular use of any medication having effluence to Platelet function.
16. Exposure to Rituximab 14 weeks prior to randomization.
17. Treament with Chinese medicine within 1 week before randomization.
18. Use of strong cytochrome P450 isoform 3A inhibitors and inducers and drugs metabolized by cytochrome P450 isoform 3A, cytochrome P450 isoform 2B6, and cytochrome P450 isoform 1A2, and are identified as narrow therapeutic drugs within 14 days or 5 half-lives, whichever is longer, prior to initiation of study treatment.
19. Prior treatment with any spleen tyrosine kinase (SYK) inhibitors (eg, fostamatinib)
20. Allergic to study drug active ingredient or excipient
21. Subjects who have participated in clinical studies of drugs or invasive medical devices within 4 week before randomization
22. Subjects have severe psychological or mental abnormalities
23. Alcoholic or drug abuser
24. Female subjects during pregnancy and lactation
25. The investigator considered that the subjects were not suitable to participate in the study