Iron is the highest content of trace elements in the human body, involved in hemoglobin, myoglobin, cytochrome composition, the body of a variety of enzymes containing iron or need to have iron to have activity, therefore, in addition to causing anemia, iron deficiency can also affect digestion, nerves, intellect, muscular activity, immunity and other functions of the system. Specific manifestations of iron deficiency in children are as follows: 1. Symptoms and signs of anemia: pale mucous membranes on the face and lips, palpitation, shortness of breath, increased respiratory pulse. Liver, spleen, lymph nodes are normal or mildly enlarged. (2) Non-hematological changes of iron deficiency: (1) Growth and development: the weight growth rate of children with iron deficiency anemia may be lower than normal. (2) Skin and mucous membrane: there may be antinail, stomatitis, lingual inflammation, dysphagia. (3) Gastrointestinal dysfunction: gastrointestinal biopsy reveals atrophy of gastrointestinal mucosa, decreased secretion of gastric acid, and malabsorption of xylose, fat, protein, and iron. (4) Muscle function: decreased muscle movement and physical labor. (5) Intellectual changes: easy to be irritable, not interested in the surrounding environment, intelligence test found that the baby’s attention is not focused, comprehension is reduced, and reaction is slow. (6) Xenophilia: the activity of oral mucosal cytochrome oxidase decreases in iron deficiency, and the patient has xenophilia. After one day of iron supplementation, the activity of oral mucosal cytochrome oxidase recovers, and the phenomenon of xenophilia improves. (7) Changes in immune function: (1) cellular immune function is reduced; (2) leukocyte bactericidal function is reduced; (3) humoral immunity is basically normal. (8) Iron deficiency and infection: cellular immune function is reduced in iron deficiency, and it is easy to suffer from viruses, tuberculosis, fungi and other infectious diseases.