Nine months baby body development indicators are as follows: male infant length about 65.2-80.5cm, weight about 6.67-12.99kg, head circumference 41.5-49.5cm. female infant length about 63.7-78.9cm, weight about 6.34-12.18kg, head circumference 40.5-48.2cm. This stage of the baby can use fingers to pinch tiny pills or beans and other They can also grasp and stand with their knees extended and can grasp with both hands or grasp with one hand and play with the other. One hand can pick up a toy and pass it to the other hand, and both hands can work together to manipulate toys, etc. Both hands can pick up a teacup and bring water into the mouth. Secondly, this period of time, the baby began to crawl, mainly for the abdomen as the fulcrum of the prone crawl, forearm support, like a seal crawl forward. Some 9-month-olds may not appear to crawl, but develop directly from sitting to standing and walking before crawling, and some children may appear to crawl backwards. As a developmental indicator, crawling has great individual variation, and the inability of a 9-month-old to crawl and grasp a station does not necessarily mean that it is abnormal. In addition, 9-month-old babies generally care more about the surrounding environment, eyes to look around, can make “big”, “eight”, “ah” and other sounds, but also can imitate the adult Sounds and movements. However, children with mental retardation imitate less sounds and movements, and express indifference when objects are dropped and lack the behavior of looking for objects. When these conditions occur, it is important to seek prompt medical attention for examination.