Myelodysplastic syndromes (MDS) are a heterogeneous group of hematopoietic stem cell disorders that are characterized by three main features: (1) the bone marrow shows pathological hematopoiesis, including pathological hematopoiesis of the erythroid system, leukocyte system, and megakaryocytes. (2) Ineffective hematopoiesis of the bone marrow and the resulting hematocrit reduction. This includes simple erythrocytopenia, leukopenia, thrombocytopenia, and holocytopenia. It often manifests as simple erythrocytopenia and allohematocritopenia. (iii) There is a high risk of progression to acute myeloid leukemia, and according to foreign data approximately one-third of patients have to convert to acute myeloid leukemia. The disease is mostly seen in the elderly abroad, and the age of onset is younger in our China than abroad. The reason why we say that myelodysplastic syndromes are a heterogeneous group of hematopoietic stem cell diseases is that some types of myelodysplastic syndromes develop very slowly and patients can survive for years, decades or even decades, and patients eventually die of bone marrow failure and never develop leukemia. In contrast, some myelodysplastic syndromes develop rapidly, with survival without treatment lasting only a few months or 1-2 years, and most patients eventually develop acute myeloid leukemia. Myelodysplastic syndromes are not one disease, but the sum of many diseases with the same or similar clinical symptoms. Therefore, the pathogenesis of different types of myelodysplastic syndromes differs, and the treatment outcome and prognosis of the disease vary greatly. With the development of medical science in recent years, our understanding of myelodysplastic syndromes has been greatly improved, and the types of myelodysplastic syndromes such as chronic granulocytic leukemia, 5q- syndrome, and treatment-related MDS have now been separated out and treated accordingly. Because myelodysplastic syndrome is a syndrome, it is very difficult to diagnose and often results in misdiagnosis. Nowadays, the application of bone marrow cytology, flow cytology, cytogenetics and molecular biology techniques to diagnose myelodysplastic syndromes has significantly improved the correct diagnosis rate and reduced misdiagnosis. Recently, we have adopted next-generation gene sequencing methods to detect 24 genes associated with myelodysplastic syndromes and myeloproliferative disorders, which can significantly improve the diagnosis of MDS, prognostic grouping, and also predict the response to treatment with certain drugs.