Inclusion Criteria:  elderly MDS patients; aged more than 60 years old, general condition, ECOG score less than 1; normal function of heart, liver and kidney, serum bilirubin ≤ 35 umol / L; serum creatinine ≤ 150 umol / L; patients are unsuitable or unwilling to receive hematopoietic stem cell transplantation; subjects sign informed consent.  Exclusion criteria:  serious infection was not controlled before treatment; contraindications for the use of dexitabine and azacytidine; other cases that did not meet the admission criteria.