• Patients volunteered to participate in this study and signed the informed consent form.

• Age≥18 years old, no gender limitation.

• Patient has a diagnosis of primary AML or AML secondary to myelodysplastic syndrome (MDS) as determined by pathological and morphological results, according to World Health Organization (WHO) 2016 classification.

• Patient is refractory to or relapsed after first-line AML therapy (with or without HSCT).

∙ Refractory to first-line AML treatment is defined as: the patient did not achieve complete remission/complete remission with incomplete hematologic recovery/complete remission with incomplete platelet recovery (CR/CRi/CRp) under initial therapy. A patient eligible for standard therapy must receive at least 1 cycle of an anthracycline containing induction therapy in the standard dose for the selected induction regimen. A patient not eligible for standard therapy must have received at least 1 complete block of induction therapy seen as the optimum choice of therapy to induce remission for this patient as per investigator's assessment.

‣ Early relapse after first-line AML therapy is defined as: the patients achieved CR/CRi/CRp after first-line treatment, and relapsed within 6 months with hematological relapse.

‣ Advanced relapse after first-line AML therapy is defined as: the patients achieved CR/CRi/CRp after first-line treatment and relapsed after 6 months with hematological relapse;

• Patient is positive for FLT3 mutation in bone marrow or whole blood.

• Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2.

• Patient is eligible for pre-selected salvage chemotherapy according to investigator assessment.

• Patient must meet the following criteria as indicated on the clinical laboratory tests:

∙ Serum aspartate aminotransferase and alanine aminotransferase ≤ 3.0 x upper limit of normal (ULN);

‣ Serum total bilirubin ≤ 1.5 x ULN;

‣ Serum creatinine ≤ 3.0 x ULN or an estimated glomerular filtration rate of \> 30 mL/min.

• Patient is suitable for oral administration of the study drug.

⁃ Female or male patient of childbearing age agree to take effective non-drug contraception from the date of signing an informed consent to 180 days after the last dose and will not donate sperm or eggs.