The purpose of this study is to evaluate efficacy and of safety QL0911 in the treatment of thrombocytopenia in pediatric patients with previously treated chronic ITP.

Inclusion Criteria:

1. Age ≥ 1 years old and < 18 years old.
2. Diagnosed primary ITP for at least 12 months;
3. Had received at least one first-line ITP treatment with no response or recurrence after treatment;
4. Had a platelet count <30×10^9/L within 48 hours before the first dose;
5. Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2;
6. Patients of child-bearing potential must agree to use effective contraception during the study and for 3 months following the last dose of study treatment.

Exclusion Criteria:

1. Had a history of bone marrow stem cell abnormalities or myelodysplastic syndrome other than ITP-specific changes.
2. Underwent splenectomy within 12 weeks before the first dose;
3. Had received ITP treatments (including rescue treatment) within 2 weeks before the first dose;
4. Had received romiplostim (Nplate®) or eltrombopag (Revolade®), rhTPO or other agents that stimulate TPO receptors (also known as c-Mpl)within 4 weeks before the first dose;
5. Had received antibody-based therapies within 14 weeks before the first dose.
6. Patients with concurrent or past malignant disease.
7. Serum creatinine or total bilirubin >1.5*ULN) alanine transaminase (ALT) or aspartate transaminase (AST) >3* ULN.
8. Had received antibody-based therapies within 14 weeks before the first dose.
9. Had prothrombin time (PT) or prothrombin time-international normalized ratio (PT-INR) or activated partial thromboplastin time (APTT) exceeded 20% of the reference range of normal values.