The red bone marrow is mainly found in the cancellous bone of the human body, and its distribution varies at different ages and in different physical conditions. In fetuses and young children, all of the bone is filled with red marrow, that is, inside the marrow cavities of the long bones and the cavities of the osteophytes. However, around the age of six, the red marrow inside the marrow cavity of the long bones gradually changes to yellow marrow, while the red marrow remains inside the osteophytes of each type of bone. This part is mainly located at the ends of the long bones, that is, inside the epiphysis. If the bone here is cut open, it is obvious that the internal bone is loose and there are obvious cavities, and inside the cavities is where the red bone marrow is located. In clinical practice, if a patient’s red bone marrow needs to be tested, a bone marrow puncture, such as such a puncture in the iliac bone, sternum, or lumbar spine, is required to extract the red bone marrow to help diagnose the disease. However, in times of massive blood loss or anemia, a portion of the yellow bone marrow inside the body is converted back into red bone marrow to restore the blood production function.