The vast majority of patients with ALL will die of the disease, and no standard chemotherapy regimen were defined for patients with relapsed/refractory ALL.Our previous experience has shown that Cladribine in combination of GAP (G-CSF priming, low dose cytarabine, and Pegaspargase) 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 Pegaspargase (C-GAP) in patients with refractory/relapsed acute Lymphoblastic Leukemia