Bone age is the time of appearance, number and morphological changes in the epiphyseal ossification centers of the long bones of children of different ages as determined by X-ray examination and standardized. In simple terms, bone age reflects the maturity of the long bones, and is usually measured on right knee x-rays for infants under 6 months of age and on left wrist x-rays for infants over 6 months of age and older children. The number of ossification centers in the wrist from 1 to 9 years old is approximately the number of years plus 1. At present, we often use the G-P method and TW3 method to make a comprehensive judgment. Skeletal development is closely related to the endocrine system and is not significantly associated with heredity or race, so bone age determination provides a good understanding of the stage of growth and development and the nutritional and disease status of each individual. For example, children with growth hormone deficiency tend to be behind in bone age, while children with precocious puberty show accelerated bone age, and children with familial short stature have bone age that matches their actual age. Therefore, the clinical determination of bone age is of great importance.