This research study is studying a drug called Jaktinib as a possible treatment for Myelofibrosis.

This study is a Phase 1, single-arm, open-label, dose escalation trial, to evaluate the safety and tolerability of Jaktinib in patients with PMF or Post-PV/ET MF and who are relapsed/refractory to a marketed JAK inhibitor

Inclusion Criteria:

• Diagnosis of myelofibrosis (primary, post-polycythemia vera, or post-essential thrombocythemia).
• Relapsed/refractory to a marketed (FDA approved) JAK inhibitor.
• At least 18 years of age.
• ECOG PS 0, 1, or 2.
• Expected life expectancy is greater than 24 weeks.

Exclusion Criteria:

• Any chemotherapy, immunomodulatory therapy, immunosuppressive therapy, corticosteroids, or growth factor treatment within 14 days prior to initiation of study drug.
• Major surgery or radiation therapy within 28 days prior to initiation of study drug.
• With suspected allergies to jaktinib or its excipient.
• Another clinical trial of a new drug or medical instrument within 3 months before screening.
• Females who are pregnant, currently breastfeeding, planning to become pregnant.
• Unable to adopt effective contraceptive methods during the study.