This study is a single-center, single-arm, prospective phase II clinical trial that evaluates the efficacy and safety of an reduced-intensity conditioning (RIC) regimen with thiotepa combined with busulfan, fludarabine, and cytarabine for allogeneic hematopoietic stem cell transplantation in the treatment of relapse and refratory peripheral T-cells lymphoma. The conditioning regimen includes thiotepa at a dose of 5mg/kg/d at d -7 (1 day), fludarabine at 30mg/m2/d from d -6 to d -2 (5 days), cytarabine at 1g/m2/d from d -6 to d -2 (5 days), and busulfan at 3.2mg/kg/d from d -4 to d -3 (2 days). Conditioning begins on day -7, and donor hematopoietic stem cell infusion is performed on day 0. All patients will undergo bone marrow examination on day 14 and day 28 post-transplant, followed by bone marrow examinations every 30 days within the first year after transplantation, and every 60 days within the second year after transplantation. FDG-PET/CT imaging will be adopted every 6 months after transplantation. If disease relapse is suspected during the follow-up period, bone marrow and relapse site examinations will be conducted at any time. The primary study endpoints are the 1-year and 2-year progression-free survival (PFS) rates post-transplant. Secondary study endpoints include the incidence of acute graft-versus-host disease (GVHD) within 180 days post-transplant, cumulative relapse rates at 1 year and 2 years post-transplant, 1-year and 2-year overall survival (OS), graft-versus-host disease-free, relapse-free survival (GRFS), non-relapse mortality (NRM), cumulative incidence of chronic GVHD, and the incidence of Cytomegalovirus （CMV）and Epstein-Barr virus（EBV）reactivation within 1 year.