CAR-T cells therapy is the preferred option for relapsed/refractory B cell leukemia/lymphoma. However, some patients will relapse after CAR-T cells therapy, and because of previous multicycles chemotherapy it's very difficult to abtain enough lymphocytes for preparation of antologous CAR-T cells. The exploration of alternative source of lymphocytes for CAR-T cells preparation has important clinical implications for such patients. We evaluated the efficacy and safety of cord blood-derived CAR-T cells in such patients, and to explore effective treatment options for such patients.