1. Infection: After a patient receives a hematopoietic stem cell transplant, the chance of infection increases significantly due to the suppression of immune function, with an incidence of 50% to 80%. Infectious lesions may occur in any part of the body and may arise from complications of transplantation operations, activation of potentially infectious agents, and exposure to new pathogens in the environment. The pathogens that cause infections include bacteria, fungi, viruses, and parasites. Infection remains one of the major factors currently affecting the long-term survival of transplanted individuals. 2. Graft failure: It is one of the most serious early complications of hematopoietic stem cell transplantation. Due to the failure of graft implantation and hematopoietic reconstruction, the clinical presentation of patients with severely reduced complete blood picture with bone marrow emptiness or hypoplasia, infection and bleeding complications, difficult management and high mortality. However, with the continuous progress of transplantation technology, the incidence of graft failure has been reduced to less than 5%, or even lower. GVHD is a major complication of hematopoietic stem cell transplantation and a cause of death, and its occurrence is related to immunogenetic differences between the donor and recipient. Chronic GVHD is a systemic disease similar to autoimmune disease, often involving multiple organs. 4. Hemorrhagic cystitis: It is one of the common complications of hematopoietic stem cell transplantation and is caused by damage to bladder mucosa by chemotherapeutic drugs used for pretreatment, with clinical manifestations of varying degrees of hematuria, which can be cured in most patients after treatment with massive infusion and alkalinization of urine. The incidence and severity of hemorrhagic cystitis are reduced to a lower level due to the application of drugs for prevention during transplantation at present. 5. Distant comorbidities: mainly involving respiratory and pulmonary diseases, hypothyroidism, hypogonadism, cataracts, secondary second tumors, etc. These comorbidities are mainly due to the toxic side effects of radiotherapy and chemotherapy during the transplantation process, and the incidence is not high.