Baby more than 8 months to sit unsteadily, may be due to the lack of exercise, or due to the lack of certain trace elements, rickets and other factors. 1. Lack of exercise: If the usual exercise about sitting and standing is relatively small, the baby lacks the awareness of exercise and may not be able to sit steadily. Insist on practicing sitting for a period of time, the symptoms will be relieved by themselves. 2. Lack of micronutrients: a long time lack of vitamin D, calcium, may affect the development of bones, in 8 months may appear to sit unsteadily, the development is also slower than the same age. 3. Rickets: long-term large-dose deficiency of vitamin D may directly cause rickets, resulting in weakened bone support capacity, easy to cause bone deformity and softening, so there will be the phenomenon of unsteady sitting. In severe cases, it will also affect limb movement. Babies 8 months unsteady sitting may also be the brain neurodevelopmental abnormalities, increased muscle tone, hypothyroidism and other factors, it is recommended to consult a doctor as soon as possible to analyze the cause of the disease, and then timely treatment.