High platelets in children’s physical examination may be physiologically elevated or secondary to elevated platelets, or it may be due to hematological disorders such as myeloproliferative neoplasms. Platelet count in human blood is in a state of dynamic equilibrium, i.e., new platelets are constantly generated in the bone marrow, while the senescent platelets will be destroyed by the spleen. When more platelets are generated in the bone marrow than destroyed, there may be a temporary elevation, which can be restored to normal on its own. In normal people, platelet count fluctuates from 6.0% to 10% per day, is higher in the afternoon than in the morning, is higher in winter than in spring, and is elevated after strenuous activity and a full meal. This is a physiologic increase and is normal. When bleeding occurs in human body, in order to stop bleeding as soon as possible, platelet generation in bone marrow can be elevated, which leads to a temporary increase in platelet count in peripheral blood, secondary platelet elevation, platelet count can be gradually restored to normal after hemostasis. When primary thrombocythemia occurs in human body, the platelet count can be high at the early stage of the disease, but there are no secondary factors such as bleeding, and it is persistently elevated, so it is feasible to make a clear diagnosis by bone marrow aspiration. It is recommended that patients with high platelet count should consult the hematology department in time to identify the specific cause of the disease and then treat the cause.