Head circumference of children reflects the development of brain and skull, and the size of head circumference is related to the head circumference of both parents, and the normal rule is that the smaller the child, the faster the growth rate. The average head circumference of a full-term newborn is 34 cm and reaches 46 cm at the age of one year. from the second year onward, the growth rate of head circumference slows down and is about 48 cm at the age of two, 50 cm at the age of five, and 54-58 cm at the age of 15, which is close to the adult level. Measuring head circumference within two years of age is the most valuable and meaningful.