The causes of bleeding spots under the skin of children are as follows: 1. Damage to the blood vessel wall is the main cause of subcutaneous bleeding, because after the damage to the blood vessel wall, blood can seep from the blood vessel to the outside of the blood vessel, which is manifested as the bleeding and purpura of the skin seen in the clinic. Damage to the vessel wall can be caused by many reasons, including drugs such as sulfonamides or insect bites that can lead to allergic purpura. In addition, bacterial and viral infections can also cause damage to the vascular wall of the skin, resulting in the bleeding spots, petechiae, ecchymosis and purpura seen clinically. In addition, malnutrition, vitamin C deficiency can lead to skin vascular wall damage, resulting in skin bleeding, as well as the rare hereditary hemorrhagic capillary dilatation can cause increased vascular wall fragility, resulting in the appearance of subcutaneous bleeding spots; 2, platelet factors, platelets play an important factor in the process of hemostasis, when children occur immune thrombocytopenia, when the number and quality of platelets are abnormal when the skin mucosa bleeding is easily caused. There are many causes of platelet quality and quantity alterations, which in children mainly include immune thrombocytopenia, aplastic anemia, leukemia, etc.; 3. Coagulation and anticoagulation factors. Lack of coagulation factors or excessive anticoagulation factors in the blood can easily lead to abnormalities in the coagulation and anticoagulation mechanisms and result in skin bleeding, such as diffuse intravascular coagulation. When children have subcutaneous bleeding spots, in addition to understanding the skin bleeding spots, we should also pay attention to whether there is gum bleeding and nasal bleeding. Pay attention to understand the medical history, whether it is collision or spontaneous bleeding, and whether there is a combination of fever, anemia and other clinical manifestations. Children with subcutaneous bleeding spots should go to the hospital promptly for platelet count, coagulation function test, capillary fragility test, etc. According to the results, the specialist will make the appropriate diagnosis and give the correct treatment.