Disclosed is the use of a water-soluble realgar solid dispersion in the preparation of an erythroid differentiation inducer for bone marrow hematopoietic stem cells and/or bone marrow hematopoietic progenitor cells. The water-soluble realgar solid dispersion is prepared from raw materials comprising 1 part by weight of realgar, 1-20 parts by weight of a polymer, and 0-5 parts by weight of a surfactant. The water-soluble realgar solid dispersion can induce bone marrow hematopoietic stem and/or progenitor cells to be differentiated into red blood cells, promote the accumulation of red blood cells in bone marrow cells, effectively alleviate the decrease in the number of red blood cells caused by the suppression of the erythroid differentiation of bone marrow hematopoietic stem and/or progenitor cells, improve anemia caused by hematopoietic failure, and protect bone marrow cells from the killing effect.