In allogeneic hematopoietic stem cell transplantation (allo-HSCT), the conditioning regimen plays a crucial role in the transplantation process, aiming to eliminate any leukemia cells and suppress the recipient's immune system to promote engraftment. Conditioning regimens are categorized into myeloablative (MAC), non-myeloablative (NMA), and reduced-intensity conditioning (RIC) based on their intensity. The choice of regimen depends on disease type, patient age, comorbidities, and donor source. The conditioning regimens vary between matched sibling donors and alternative donors. In haploidentical transplantation, the mainstream non-T cell depletion protocols included the granulocyte colony-stimulating factor (G-CSF)/antithymocyte globulin (ATG)-based and post-transplantation cyclophosphamide (PT-Cy)-based strategies. In hematologic non-malignancies such as aplastic anemia, Fanconi anemia, and thalassemia, the tailored conditioning regimens are crucial for improving outcomes. The diversified and personalized conditioning regimens are the future direction in the field of transplantation. Future directions may include integrating new targeted therapies and immunotherapies into conditioning regimens to further optimize outcomes.