This trial is a prospective, single-arm, single-center clinical study. A total of 44 elderly (aged 60 to 69 years) patients with hematological malignancies who need to receive a single-unit unrelated umbilical cord blood transplantation (UCBT) are planned to be enrolled. After screening and enrollment, patients are scheduled to receive the following drug treatment regimen: Thiotepa 5 mg/kg every 12 hours on day -8; Granulocyte Colony-Stimulating Factor(G-CSF) 5 ug/kg/day from day -8 to -5; Cytarabine 1.5 g/m2 from day -7 to -5; Fludarabine 30 mg/m2/day from day -7 to -4; Busulfan 0.8 mg/kg every 6 hours from day -4 to -2. Umbilical cord blood hematopoietic stem cells are reinfused on day 0. Routine monitoring of blood routine is conducted, and platelets and red blood cells are transfused when necessary.