Caries (tooth decay) is a very common oral disease, which seriously endangers people’s physical and mental health. Its occurrence is the result of the joint action of many factors. When the food enters the mouth, the sugar in it is used by the bacteria in the mouth to produce many kinds of organic acids, and these organic acids invade the tooth tissue to cause tooth demineralization, thus producing caries. The harm of children’s caries mainly has the following aspects: 1. Under each milk tooth there is a permanent tooth embryo developing. The development of caries in milk teeth leads to pulpitis and periapical inflammation, which will make the infection develop to the deep and affect the normal development of permanent tooth embryo. In the light case, it may cause the permanent teeth to be poorly calcified and prone to caries; in the heavy case, it may terminate the development of the permanent tooth embryo due to the destruction of infection and cause the permanent teeth to be congenitally missing. In addition, the premature loss or extraction of the baby teeth due to serious caries often causes the displacement of the neighboring teeth, resulting in the disorder of the eruption of permanent teeth, and causes the teeth to be misaligned, which not only affects the beauty, but also susceptible to caries and periodontal diseases. 2.The normal development of children depends on good digestion and absorption. As the first step of digestion, chewing food is very important to the good absorption of nutrition. Due to the decay of milk teeth and can not effectively cut and chew the food, it will definitely affect the normal nutrition absorption and make the nutrition disorder, thus affecting the growth and development of the whole body. 3.Good chewing is a necessary stimulus for the development of jaw bone. Children are often afraid to chew with the affected teeth because of pain, which causes underdevelopment of the jawbone and affects the formation of normal facial appearance, and also causes crowding of permanent teeth arrangement. Over time, it will develop the habit of chewing on the side and cause the asymmetry of facial development. 4.Chronic inflammation such as caries, pulpitis and periapical inflammation exist in the mouth for a long time, forming oral lesions, which may also cause infections of other organs and systems in the body. For example, the bacteria in the cavity and the toxin produced by it will reach all parts of the body with the blood flow, causing heart disease, kidney disease, eye disease and joint disease, and endangering the whole body health. 5.Dental caries can also affect children’s mental health. The painful irritation caused by caries and the unattractive and unclear speech caused by the decayed front teeth will affect the normal psychological development of children. Therefore, healthy milk teeth are a part of children’s physical and mental health, which should be paid enough attention. The view that “decayed milk teeth do not need to be treated, it will be fine when the teeth are replaced” is very wrong.