A normal blood smear in children cannot rule out a bone marrow problem, and further bone marrow tests are needed to clarify the situation. Blood smear in children is a common method of blood cytology, which can be used to detect the presence or absence of abnormal numbers or patterns of red blood cells, white blood cells, platelets, pathogens and their proportions in children’s peripheral blood, which is valuable for the diagnosis of a variety of blood disorders, such as anemia, acute and chronic leukemia, platelet abnormality, multiple myeloma, myelofibrosis and other diseases. However, the presence or absence of bone marrow abnormalities requires more accurate bone marrow cytomorphology, and bone marrow problems cannot be ruled out by blood smears alone; bone marrow aspiration is required to confirm the presence or absence of bone marrow problems.