The invention belongs to the fields of cell biology and medicine, and relates to the medical use of NOTCH4 or the medical use of NOTCH4 inhibitors. In particular, the invention relates to use of NOTCH4 protein or NOTCH4 gene for manufacture of a medicament for promoting hematopoietic stem/progenitor cell differentiation and megakaryocyte differentiation in a mammal, a medicament for treating megakaryocyte dysplasia, or a medicament for promoting platelet production. The invention can effectively promote the production of hematopoietic stem/progenitor cells and megakaryocytes in vitro, thereby significantly improving the efficiency of platelet production in vitro, and having a good application prospect.