This is a multicenter, placebo-control, phase 3 study of hetrombopag in patients with treatment-naive severe aplastic anemia. All subjects who have completed or withdrawn from the HR-TPO-SAA-III study will voluntarily participate in this extension study.

Subjects will receive the same study drug (hetrombopag or placebo) as in study HR-TPO-SAA-III, with the same doses and administration schedule or with modifications based on the actual conditions.

The primary objective of this extension study is to give the subjects participating in the HR-TPO-SAA-III study the continued access to the study drug (hetrombopag or placebo) after the completion of the HR-TPO-SAA-III study.

Inclusion Criteria:

1. Subjects who have completed or withdrawn from the HR-TPO-SAA-III study
2. Subjects who have signed the informed consent form
3. Female and male subjects of childbearing age who agree to take adequate contraceptive measures during the extension study period and within 28 days after the last dose
4. Subjects who have completed the end-of-treatment evaluation in the original study

Exclusion Criteria:

1. Any unstable situation or situation that will compromise the safety of the subject
2. Evidence of clonal cytogenetic abnormalities at the end-of-treatment examination of the HR-TPO-SAA-III study
3. Subjects with uncontrollable hemorrhage and/or infection after standard treatment
4. Subjects who have experienced deep vein thrombosis, myocardial infarction, stroke, or peripheral arterial embolism within 1 year
5. Any situation that may compromise the subject and the safety or compliance thereof during the study