The normal value of platelets is (100-300)*10⁹/L, while the children’s cold platelets 500*10⁹/L, mostly considered to be high platelets, which may be caused by primary thrombocythemia, chronic granulocytic leukemia and other diseases. 1. Primary thrombocythemia: the etiology of primary thrombocythemia is not clear, and it is considered to be related to factors such as gene mutation and clonal proliferation of bone marrow hematopoietic stem cells. Patients may have symptoms such as bleeding, thrombus, splenomegaly, etc., and the platelet count is 500*10^9/L during platelet test. If primary thrombocythemia is complicated by cold in children, the platelet value will be increased. 2. Chronic granulocytic leukemia: chronic granulocytic leukemia may be caused by exposure to hair dyes or ionizing radiation, and patients will have symptoms such as fatigue, low fever, and lethargy. Moreover, patients will have lower hemoglobin, higher platelets and higher white blood cells when doing routine blood tests. If leukemia is complicated during a child’s cold, a platelet count of 500*10⁹/L will occur during the platelet check. Children’s cold platelet 500 * 10 ⁹ / L, there may also be other reasons, such as infection caused by a transient rise in platelets, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.