Inclusion Criteria:
* Fully understand the procedures of the clinical study and participate voluntarily with signed and dated written informed consent form, comply with the requirements of the study protocol.
* Males and/or females at least 18 years old when signing the informed consent form.
* Histologically confirmed AML (defined using WHO criteria 2016) with one of the following:
Refractory to at least 1 cycle of induction chemotherapy. Relapsed after achieving remission with a prior therapy.
* Subject is positive for FLT3 mutation in bone marrow or blood after completion of the subject's last interventional treatment.
* Eastern cooperative oncology group performance status (ECOG) ≤2 at screening.
* Life expectancy of at least 3 months.
* Women of childbearing potential have a negative pregnancy test at baseline and are willing to employ an effective method of contraception for the entire duration of study treatment and 6 months after the last dose.
Exclusion Criteria:
* Known or suspected allergies to any of the investigational drug composition (HYML-122, lactose, hydroxypropyl cellulose, hyposubstituted hydroxypropyl cellulose, silicon dioxide, magnesium stearate, titanium dioxide and polyethylene glycol).
* Medical history and surgical history excluded according to the protocol.
* Any previous medical treatment history exclude from the protocol.
* Abnormal laboratory results exclude from the protocol.
* Combination of treatments and/or drugs required during the study period and cannot be discontinued that excluded from the protocol.
* Alcohol abuse within 6 months prior to screening, defined as long-term drinking history, generally more than 5 years, equivalent to alcohol quantity ≥40g/d for men, ≥20g/d for women, or heavy drinking history within 2 weeks, equivalent to alcohol quantity ≥80g/d. alcohol volume (g) conversion formula=alcohol consumption (mL)\*alcohol content (%)\*0.8.
* Abortion less than 30 days prior to screening, pregnant and lactating women (currently breast-feeding or less than one year after delivery although not breast-feeding), women of childbearing potential who are not guaranteed effective contraception during the study, planning pregnancy or donating eggs or sperm within 6 months after the last dose.
* History of drug abuse or drug addicts.
* Subjects may not be able to complete the study duo to poor compliance or other reasons, or unsuitable for the study by the investigator's judgment.
