Low platelets after transplantation are usually due to poor bone marrow implantation, drug side effects or disease recurrence. 1. Poor bone marrow implantation: poor bone marrow implantation is a common complication after bone marrow transplantation, which can be induced by factors such as graft-versus-host disease and severe infection. 2. Drug side effects: Generally speaking, low platelet after bone marrow transplantation for hematologic malignant diseases is mostly due to the side effects of pretreatment with high-dose chemotherapeutic drugs (fludarabine) before bone marrow transplantation, and the patient’s own bone marrow hematopoietic function has not been restored. In most patients, platelets will gradually recover about one month after bone marrow transplantation. If platelets are still low one year after the transplant, they can be treated with thrombopoietin or platelet transfusions to minimize the risk of bleeding. 3. Disease relapse: If platelets have returned to normal after bone marrow transplantation, but are low again, a relapse of leukemia or other hematologic diseases should be considered. The next step of treatment should be decided according to the time of relapse and the degree of relapse. If the relapse is only molecular, it can be treated with immunosuppressant (cyclosporine) tapering or lymphocyte infusion. If it is a full-blown relapse, the chemotherapy regimen will need to be adjusted. Or continue to consider hematopoietic stem cell transplantation or bone marrow transplantation, with drugs such as cytarabine and flexerodine. Disease-specific treatment should be under the direction of a physician.