In early childhood, children with mental retardation mainly show overall lag in gross motor, language, fine motor and response functions; in school age, they mainly show poor academic performance, and milder mental retardation can generally receive primary education, but it is difficult to receive middle school education. The performance of mental retardation varies according to different levels. 1, mild mental retardation: early development is slightly slower than normal children, not as lively as normal children, lack of interest in the surrounding things. They are not as active as normal children and lack interest in things around them. They may follow rules or act roughly. Speech development is slightly delayed and abstract vocabulary is poorly acquired. Poor analytical ability and superficial understanding of problems. Poor academic performance compared to average children, can recite texts but cannot use them correctly, and have difficulty in completing arithmetic application problems. 2.Moderate mental retardation: incomplete development of language function, slurred words, poor vocabulary, only simple concrete thinking, abstract concepts are not easily established. The ability to discriminate between the surroundings is poor, and they can only recognize the surface of things and fragments of phenomena. They cannot make progress in reading and calculation. 3.Severe mental retardation: vague pronunciation, very little speech, and very poor self-expression. Lack of abstract concepts and low comprehension ability. Emotionally naive. Very clumsy movements. Some defensive ability, able to avoid obvious very dangerous. 4.Extremely severe mental retardation: No understanding of everything around. Lack of language function, at most can shout “Dad”, “Mom”, etc., but can not really identify Mom and Dad, often unconscious shouting. Lack of self-protection instincts, not knowing how to avoid obvious dangers. Emotional responses are primitive. Sensation and perception are significantly diminished. Significant motor dysfunction, inflexibility of arms and legs or lifelong inability to walk. There are often multiple disabilities and recurrent seizures.