Myelodysplastic syndrome (MDS) is a clonal disease characterized by active bone marrow proliferation, peripheral blood cell reduction and abnormal cell function a malignant hematologic disorder, mainly manifested by inefficient hematopoiesis leading to bone marrow failure and peripheral blood cell reduction, with progressive disease and a high mortality rate. There is a lack of good therapeutic drugs for this disease, and the efficiency (improvement rate) of various treatments is about 30%, which is not very satisfactory and the patient’s quality of life is poor, and supportive treatment is the current standard program. Decitabine (Dacor) is a demethylating drug, which belongs to cytosine nucleotide analog, it can reverse abnormal DNA methylation, adulterate DNA sequence to capture DNA transferase and deplete intracellular DNA methyltransferase, it has higher in vivo cytotoxicity than cytarabine and azacitidine, it has stronger ability to induce cell differentiation and inhibit methylation than azacitidine, thus, it is its irreplaceable advantages and efficiency in the treatment of neoplastic diseases. The regimen of decitabine is 20 mg/m2 once daily by intravenous injection over 1 hour for 5 days, every 4 weeks. The latest data showed a complete remission rate (CR) of 39%, median onset of action of 1.7 months, median CR duration of 14 months, median survival time of 22 months, median time to progression to acute leukemia of 20 months, and an overall improvement rate of 70%. It is currently the most efficacious drug for the treatment of MDS. The overall safety of decitabine treatment is high, with a low incidence (<5%) of serious (grade 3-4) adverse reactions. The main side effects (adverse reactions) are neutropenia, thrombocytopenia, anemia and other manifestations of myelosuppression, but its treatment-related mortality is significantly lower compared with intensive chemotherapy (p=0.001). The incidence of other toxicities is relatively low and can be alleviated by symptomatic management or dose reduction or delayed dosing. Dacor is contraindicated in patients with known hypersensitivity to decitabine. In conclusion, decitabine is currently the most effective drug for the treatment of MDS, and its efficacy and safety have been recognized by clinicians and patients as a new gospel for MDS patients. It is believed that through the unremitting efforts of medical scientists, malignant blood diseases like MDS will be truly cured.