Sequence of development of sitting position: 5 months, the head, shoulders and legs can be lifted when pulling up and sitting; 6.1 months, the head can be done alone and needs to be supported by hands; (arching back sitting) 6.6 months, the head can be lifted spontaneously and repeatedly in supine position for more than 5s; 7.3 months, the head can sit straight for at least 1min without support; 8 months, the lateral support response; 9 months, the head can sit on its own; Purpose: The focus is to suppress the abnormal posture of the lower limbs, promote the straightening of the trunk and The purpose is to suppress abnormal lower limb posture, promote the development of trunk uprightness and balance reflexes, and lay the foundation for standing; Meaning: Sitting is the intermediate posture in the development of standing, and standing is impossible if you cannot do it. The ability to sit alone marks the completion of static and dynamic balance in sitting position. Japanese experts believe that if sitting can be completed before the age of 2, 95% of the children can walk independently. Conditions for sitting control ability: 1 upper limbs support the body to sitting height (improve upper limb strength, inhibit abnormal upper limb posture, promote vagus, visualization, trunk uprightness); 2 from the four crawl position alone body axis gyration (lumbar and abdominal muscle control ability, four crawl conversion to sitting position); 3 sitting balance reflex appears; 4 chain reaction of trunk muscle groups (each position to sitting posture conversion).