Abstract: Objective To evaluate the efficacy and safety of decitabine in the treatment of patients with moderate to high risk myelodysplastic syndrome(MDS), and to explore the clinical significance of TET2 and DNMT3 A gene mutations. Methods Clinical data of 81 patients with MDS in the First Affiliated Hospital of Zhejiang Chinese Medical University were retrospectively analysed. According to the different treatment methods, they were divided into single drug group(32 cases, decitabine) and combined chemotherapy group(49 cases, decitabine, homoharringtonine, Ara-C and Aclacinomycin). Results ① The efficacy:the complete remission(CR) rate was 25.0% and the overall response(ORR) was 53.1% in the single drug group. The CR rate was 44.9% and the ORR rate was 67.3% in the combined chemotherapy group. ② The progression-free survival time(PFS):the single drug group was 9 months, and the combined chemotherapy group was 13 months, with no significant difference(χ²=0.942, P=0.332). ③ Adverse events:the incidence of grade 3-4 hemocytopenia was 81.25% in the single drug group and 89.79% in the combined chemotherapy group. The incidence of infection was 65.63% in the single drug group and 77.55% in the combined chemotherapy group. The non-hematological toxicity was grade 1-2 in two groups. ④ There were 16 cases of TET2 gene mutation, including 5 cases in single drug group and 11 cases in combined chemotherapy group. There were 8 mutations of DNMT3 A gene, including 1 in single drug group and 7 in combined chemotherapy group. There was no significant difference between two groups. Conclusion Decitabine have good efficacy in the treatment of moderate to high risk MDS. There was no significant difference between the two treatment methods. TET2 and DNMT3 A gene mutations have no significant effect on efficacy.