Abstract: This study measures the dental arches of 1936 children, aged 6-12 years. The anterior dental arch increases fast from 7 to 9 years, because of the eruption of canine. It is stand still after 11 years old. During the mixed dentition period, the width of anterior dental arch increases about 2mm, and the hypotenuse about 1.8mm. The width and hypotenuse of posterior dental arch increase about 1 mm. The size of anterior dental arch in boys is larger than that in girls, less than 1 mm. Both of width and hypotenuse of posterior dental arch in boys are larger about 1 mm than in girls in all classes. From 6 to 12 years, there are the primary dental arch, the first molar dental arch and the second molar dental arch among children. Their proportions are 2.1 %, 76% and 21.9% respectively.

Key words: Children; Dental arch; Development