The symptoms of mental retardation are as follows: 1. low ability of each, early may be motor development backward, communication disorder or language development backward, for example, in early infancy can be seen when the sit can not sit, when the crawl can not crawl, when the walk can not walk, some children even to two years old can not walk, 2. The cognitive development is backward; 2, communication and social behavior does not match, such as 6-7 months old still can not recognize parents, can not distinguish between close and distant; 3, after growing up, manifested as a relatively low level of intelligence, may go to school after the learning disability, understanding ability deviation, emotional abnormalities or thinking problems.