This is an open-label, Phase I study of QN-023a (allogeneic CAR-NK cells targeting CD33) in relapsed/refractory Acute Myeloid Leukemia (AML). The clinical study is to evaluate the safety, tolerability and preliminary efficacy of QN-023a in patients with relapsed/refractory AML, where a “3 + 3” enrollment schema will be utilized at dose escalation stage. Up to 19 patients will be enrolled. The gene discussed is CD33; the disease is acute myeloid leukemia.