There is no absolute standard for the development of a nine-month-old baby, but it can generally be analyzed in terms of height, weight, head circumference, gross and fine motor movements and language as follows: 1. Height: the average height of a nine-month-old male baby is 65.2-80.5cm, and the average height of a female baby is 63.7-78.9cm. 2. Weight: The average weight of nine-month-old male babies is 6.67-12.9kg, and the average weight of female babies is 6.34-12.2kg. 3. Head circumference: the average nine-month-old male baby is 41.5-49.4cm; the average female baby is 40.5-48.2cm. 4. Gross and fine motor: can try to stand alone, can take out toys from drawers to play, etc. 5. Language: can understand a few more complex words and phrases, such as “goodbye” and so on. Nine-month-old baby’s development is multi-faceted, in addition to the above performance, will be manifested in other. There is no absolute standard. However, if the baby’s development is significantly later than that of babies of the same age, it is recommended to consult a doctor in time.