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.