Decitabine is a specific DNA methylation transferase inhibitor. Unlike conventional chemotherapy, which exerts its anti-tumor cell effects through cytotoxic effects, decitabine exerts its anti-tumor effects through demethylation and activation of oncogenes to re-express them. In addition, decitabine can substantially enhance the sensitivity of tumor cells to T-lymphocyte killing, and at the same time, decitabine promotes the expression of important tumor antigens in leukemia cells by inducing the expression of immune activating molecules, thus enhancing the function of tumor immunity of the body. In clinical practice, decitabine is widely used in the treatment of various types of myelodysplastic syndromes, while in recent years, decitabine has also been used in the treatment of elderly leukemia patients and has achieved good therapeutic effects.