Infant platelets 1200×10^9/L is more serious, the cause should be clarified in time and standardized treatment should be carried out so as not to jeopardize the health of infants. The normal range of platelets is around (100~300)×10^9/L. Infantile platelets 1200×10^9/L is more serious, indicating the presence of thrombocytosis. It may be secondary to other diseases, such as primary myelofibrosis, myelodysplastic syndromes, chronic myeloid leukemia, and true erythrocytosis, or it may be due to infection, anemia, or blood loss. Infant platelet 1200×10^9/L should be further examined in time, including blood smear examination, bone marrow aspiration smear, platelet and coagulation function test, C-reactive protein and hemoglobin sedimentation rate. Infant platelets 1200 x 10^9/L should be taken seriously and treated according to medical advice to minimize the adverse effects on infants.