Inclusion Criteria:  Patient age ≥ 18 to ≤ 60 years ECOG score 0-2 points/Karnofsky score ≧80 To receive allogeneic hematopoietic stem cell transplantation from related haploid or unrelated donor The pretreatment of modified Bu/Cy+ATG scheme was planned. Patients with malignant hematological diseases indicated by transplantation and in CR state Expected survival ≥ 3 months Signed written informed consent (Patient must be capable of understanding the investigational nature, potential risks and benefits of the study, and able to provide valid informed consent) Agree to use effective contraception  Exclusion Criteria:  Prior allogeneic hematopoietic stem cell transplant Allergy/intolerance to Sitagliptin There are contraindications for Sitagliptin use. Moderate or severe renal insufficiency Patients with diabetes mellitus requiring insulin secretagogues and/or insulin Human immunodeficiency virus or active hepatitis C virus or active hepatitis B virus infection Active infection that is difficult to control Vital organ function cannot tolerate transplantation Other malignant tumors outside the blood system, except the following diseases: malignant tumors that have been cured for 3 years without active lesions; Adequate treatment of non-melanoma skin cancer without active foci of malignant amygdala and carcinoma in situ There is evidence that may interfere with the study or make patients at risk of serious complications or medical conditions, including but not limited to serious cardiovascular diseases (such as New York heart association class III or IV heart disease over the past six months of myocardial infarction, unstable type of cardiac arrhythmias) or unstable angina and/or severe lung disease (e.g. History of severe obstructive pulmonary disease and symptomatic bronchospasm) Pregnant or lactating women Any life-threatening medical condition or organ system dysfunction considered by the investigator may endanger the patient's safety by interfering with the absorption or metabolism of sitagliptin or putting study results at unnecessary risk