AML is most common in the elderly patients, who can not tolerate the intensified treatments. The vast majority of patients with AML will die of the disease, and no standard chemotherapy regimen were defined for patients with relapsed/refractory AML. Previous studies have confirmed the efficacy of cladribine in the treatment of AML, both de novo or relapse/refractory AML. Our previous experience has shown that Cladribine in combination of CAG (G-CSF priming, low dose cytarabine, and aclarubicin) are effective with tolerable toxicity profiling.Thus, this phase 2 clincial trial is going to evaluate the efficacy and safety of cladribine in combination with G-CSF, low-dose cytarabine and aclarubicin (C-CAG) in patients with refractory/relapsed acute myeloid leukemia.