Allogeneic hematopoietic cell transplantation (allo-HCT) is the only treatment that offers a possible cure for relapsed/refractory AML. Currently, the optimal preallo-HCT bridging regimen for relapsed/refractory AML patients is unclear. Venetoclax-based regimens, including Venetoclax + demethylating agents (HMA) , Venetoclax + HMA + other drugs and Venetoclax-based multidrug combinations as a bridging regimen improves response rate and post-transplant survival in relapsed/refractory AML patients. Therefore, the investigators conduct a prospective single-centre clinical study to evaluate the efficacy and safety of VAH as a transplant bridging regimen for relapsed/refractory AML.