Lead is a toxic heavy metal, and long-term exposure to lead in children can cause functional impairment of multiple systems. The normal value of blood lead is generally below 100ug/L. The CDC in the United States diagnoses blood lead level ≥100ug/L as lead poisoning regardless of whether there are clinical symptoms as well as various physical signs. According to the blood lead level, there are five levels: Level I, which is blood lead below 100ug/L, is a relatively safe blood lead level and does not require clinical treatment. Level 2, which is a general blood lead level of 100-199ug/L, is a mild lead poisoning and requires dynamic observation of the blood lead level. Grade III, blood lead level is 200-449ug/L, which is moderate lead poisoning. Grade IV, blood lead level of 450-699ug/L, needs to be rechecked within 48 hours, belongs to severe lead poisoning. Grade V, blood lead level is greater than 700ug/L, which is very severe lead poisoning.