The tooth surface where the caries of the milk tooth series occurs is different according to the upper and lower jaw, as follows: 1.Maxillary milk teeth: the milk incisors are mostly found on the proximal mesial surface, followed by the distal mesial surface and the labial surface; the milk lateral incisors are mostly found on the proximal mesial surface and the labial surface; the milk cusp teeth are mostly found on the labial surface, followed by the distal mesial surface; the first milk molar is mostly found on the jaw surface, followed by the distal mesial surface; the second milk molar is mostly found on the jaw surface and the proximal mesial surface; 2.Mandibular milk teeth: the milk incisors and the milk lateral incisors are less caries-prone. The incisors are less likely to suffer from caries, and the caries is mostly found on the proximal mesial surface. The papillary cuspids are mostly found on the labial surface, followed by the distal mesial surface and proximal mesial surface; the first milk molar is mostly found on the jaw surface, followed by the distal mesial surface; the second milk molar is mostly found on the jaw surface, followed by the proximal mesial surface. In addition, the occurrence sites of milk teeth caries in each age group also have obvious characteristics. 1-2 years old children mainly occurred in the labial surface and adjacent surface of maxillary milk front teeth, 3-4 years old children mostly occurred in the sulcus of maxillary surface of milk molar, 4-5 years old children mostly occurred in the adjacent surface of milk molar.