3-4 months old baby can not maintain sitting position, this age vertical head stability, cervical spine physiological bending formation, but the thoracic and lumbar spine physiological bending is still not formed, as well as lumbar and abdominal muscle strength is not enough, so can not maintain sitting position. At this age, the main exercise is prone, head up, as well as roll over and hands to actively grasp the consciousness of objects, not yet need to exercise the sitting position. Sitting position can generally be maintained at about 6 months of age, at 7 months of age can maintain a straight waist sitting position, 8-9 months of age can be free sitting position, so the development process to follow certain growth and development rules can not be premature intervention, premature intervention is easy to damage the baby’s bones.