<p>Immune reconstitution (IR) is a critical factor influencing the quality of life and long-term prognosis in hematopoietic stem cell transplant (HSCT) recipients. But delayed IR post-transplant may lead to infections and disease recurrence, while impaired reconstitution is closely associated with graft-versus-host disease (GVHD). To formulate strategies that promote immune recovery, it is crucial to understand the fundamental principles and influencing factors of IR. The emergence of technologies such as single-cell sequencing enables researchers to reveal the specific patterns and mechanisms of immune reconstitution under different conditions, which has given us a better understanding of immune reconstitution than before. Current evidence indicates that delayed IR is related to several aspects, mainly the strength of the conditioning regimen, the composition of the graft, and the occurrence of GVHD. This review summarizes the main characteristics of immune reconstitution after allogeneic hematopoietic stem cell transplantation, combined with the latest research progress Carefully explore the influencing factors of immune reconstitution and the existing monitoring methods.</p>