To investigate safety, tolerability of cafusertib combination with low dose cytarabine (LD-Ara-C) in Chinese patients with relapsed/refractory AML that are not eligible for conventional or intensive treatment. The dose of cafusertib will be escalated to determine the dose limiting toxicity (DLT) and the maximum tolerated dose (MTD) of cafusertib in combination with LD-Ara-C in AML patients. At the same time, pharmacokinetic characteristics and preliminary efficacy of cafusertib will be observed in AML patients. To determine the recommended dosage regimen for phase II.