In adults, the bone marrow is the main hematopoietic organ of the human body. The bone marrow is located in the bone marrow cavity, especially in the flat bones, the ends of the long bones and the irregularly fixed bone marrow, which is the main hematopoietic organ, especially the sternum, which is a block of flat bones, is the most vigorous hematopoietic part of the human body, and it has the function of lifelong hematopoiesis. Before birth, during the fetal period, the fetal liver is the main blood-producing organ, and after birth, the bone marrow becomes the main blood-producing organ. As the human body ages, the hematopoietic function of the bone marrow gradually decreases, and some of the red marrow gradually becomes fatty and turns into yellow marrow and loses its hematopoietic function. However, when there is acute blood loss, some of the yellow marrow becomes red again, thus performing its hematopoietic function. Therefore, in adults, the bone marrow is the main blood-producing organ.